Aspects of Fainting

Yesterday, I had my regularly scheduled platelet donation and afterwards I fainted. This is uncommon for platelet donors, but it does occasionally happen and, as I discovered, causes quite the flurry of activity at the donation centre. Note to self: no mater how busy it is at work, don’t miss lunch on donation day.

I was curious about some of the symptoms I experienced during my slow faint:

  1. They said I had gone ash white, suggesting my blood pressure had momentarily dropped. So why did I feel super-heated? They were covering my head and neck with cold compresses and fanning me. If my blood pressure tanked, wouldn’t I feel cold not hot?

  2. I temporarily lost my hearing. It was like watching TV with the sound turned way down. Why was this?

  3. A volunteer (also a pre-med student) mentioned that if you’re fainting and you see “white spots” it means your blood pressure has dropped, if you see “black spots” your blood pressure has spiked. Is this true or just an urban legend she picked up from a misinformed first aid instructor? (I may have reversed what she said, because I was a bit whoozy at the moment and may be misremembering. It may be the other way around white=spike and black=drop)


You should probably take a 64 pack on those days.

pilots who perform high-g maneuvers report greyout, which is loss/reduction of low blood flow to the head. Basically, your eyes aren’t getting enough oxygen to work properly. I’d guess that with a lack of proper oxygenation after donating, your ears are experiencing something similar.

Based on the greyout/blackout associated with G-LOC (see first link), I think you may be misremembering, and she may be misreporting. Pilots doing high negative g’s report redout due to excessive blood pressure in the head; I can’t think of a blood-pressure-related condition that would cause one to see white spots.

Just as an aside, in my experience as a former pre-med student, pre-meds are no more knowledgable about medical matters than any other reasonably literate person, maybe less so.

The greyout as described in the article was exactly what I experienced. It’s unusual for platelet donors to faint, but given my stupid eating for the day and that they additionally took a baggie of plasma, it must have been just right to tip the scale and put me into “Wow, I feel awful” territory.

In this case, she was actually quite knowledgeable. Pre-med in Canada may be different than in the U.S. For example my former roommate’s “pre-med” was to get a degree in kinesiology with a minor in some kind of applied sciences. She practiced as a physio therapist for a bit in order to save up for med school, planning to go into sports medicine. The discussion about seeing spots took place when I was still not hearing and the room was spinning which is why I think I misremembered what she was saying. She had taken part in a blood pressure experiment involving some kind of spinning inversion table and she was talking about the the results and comparing them to what she’d learned in a first aid course about fainting. Unfortunately, it was hard for me to follow her enthusiastic chatter in my state, while I was devoting all my concentration to not puking.

And quite interestingly, she is a long-time donor and blood collection volunteer from the UK. She can no longer donate though, now that she is in Canada and banned from doing so. But she had a lot of really interesting information on the UK system and prion diseases. That conversation was more interesting because by then I was no longer feeling half-dead.

Edit: Does anyone know why I felt so hot when my blood pressure dropped? I would have expected to feel cold.

Funnily enough, I almost fainted yesterday morning, too. I gave my finger a good cut while loading the dishwasher, and while the pain or the sight of my own blood doesn’t bother me, I still tend to pass out after an injury. I usually get the greying out you mention, plus a whooshing/whirling sensation; once the world starts to get unreal, I know it’s time to lay down or put my head between my knees. I’ve also been told that I go white as a sheet before I pass out.

I wasn’t warm when I was greying out, but I got the cold shakes afterwards.

Ah, that might explain it then. In the US, pre-med generally means a mish-mash of courses focusing heavily on sciences (chemistry, physics, ect) as a part of a degree program. For instance, I was a pre-med with a major in zoology. But except for volunteer work or course work outside the major, there’s generally no medical training.

Sorry for the hijack.

I’ve only ever passed out from pain, but I saw copious silver spots, only a couple at first, and building up until everything went blank. My hearing also cut out towards the end. I’ve come close to fainting from laying on my back wrong (yay, pregnancy weirdness!), and had the silver spots and hearing loss. I spoke up about them that time, though, and they had me roll on my side and it all went away, normal as ever, within a few breaths.

I’ve fainted from low BP and experienced the same - white spots and loss of hearing. I’ve also fainted from the heat and at that time experienced black spots and no hearing loss. YMMV.

I’m afraid I’m the one who caused the confusion because I thought “pre-med” would be more helpful as a descriptive term. I may have erred. The Canadian system is basically quite similar. Some universities do offer pre-med/health combinations designed for students who intend to go on to medical school, but technically, you could get a degree in art history and then go write the MCAT. YMMV depending on the institution.

Some Canadian “pre-med” programs are often undergraduate degrees in “Medical Education” Universities with med schools are fond of offering that one. At my alma mater, the Faculty of Applied Health Sciences had a Pre-Health Professions Specialization (Honours BSc) OR you could go a totally different route through the Faculty of Science and just get your undergrad degree in Biomedical Sciences. Lots of different options.

I can only offer my opinion based on my own experiences, which is those who started out in a program like my roommate’s (kinesiology) seemed to have practical skills fairly early on, rather than just the cumulative science knowledge that you get studying for a biology degree. So when I think “pre-med” I associate with the more practical health studies, like the route my roommate took, and that may not be correct when it comes to how everyone understand “pre-med”. Oops.

It depends on how pre-med is defined. As graduate students in Toronto, my colleagues and I were responsible for most of the marking of undergraduate work in our department. On more than one occasion, we would assign an appropriate grade for work submitted and received complaints that the mark was too low. The excuse offered would be: ‘you can’t give me a “C”, I’m pre-med!’ (Not with this level of work you aren’t.)

We would then have to gently point out that until they graduated and wrote their MCATs they weren’t pre-anything and they needed to actually gasp study in order to do well in the introductory astronomy courses they were using as an “easy” science credit.

Eats_Crayons’ roommate I would happily call pre-med; the whining students in my experience who self-identify as pre-med, not so much.

And on the topic of fainting: I haven’t completely passed out after a shot or bloodwork, but I do scare the nurses frequently if I get a needle stick on an empty stomach (any needle stick). I experience similar things: the sound level outside my head goes way down, vision gets staticky, tunnels, and grays out, and I feel the need to get horizontal before the choice is taken from me. I know this so when I get vaccinated I make sure I’ve recently eaten. For fasting blood work and similar, I let the nurse know that I get faint afterwards, and they usually can find me a spot to recover and not totally pass out.


I’ve luckily never passed out, but I’ve come close a few times, most often after returning to exercising after a long absence and overdoing it.

In my experience, I get cold and clammy, not hot. I’m sure I turn pretty white (well, whiter anyway; I’m already pretty pale). My hearing is affected (just like turning down the volume) and I see what I call “bug wars” - similar to the noise you get on the TV when a station isn’t coming in. I also feel pretty nauseated, like I’m about to throw up.

Like I said, I usually only experience this when overdoing it at the gym after some months of couch-potatoing, but I also almost passed out once from what I can only characterize as stress. It happened when my mother was in the emergency room after a car accident - I was the first to arrive and they let me in to see her and give her what comfort I could. I’m not the squemish type, but apparently seeing her on the gurney while they were stitching up a gash on her head and the bone in her index finger where it’d been broken was too much for me. I felt horrible for leaving her with my husband, but I had to get out and go sit down before there were two of us that they had to care for. Apparently I turned pretty white, because some aide brought me some ice chips while I sat outside the ER getting myself together. Once I was over it, I went back in and could be by Mom’s side, no problem.

Re a point raised by **RoniaBorkason, **and perhaps of interest to those in this thread, I have just started a new thread regarding fainting specifically from pain.

I’ve suffered with low blood pressure most of my life and have had a lot of experience with fainting. On average I probably grey out about once a week and have a total blackout about twice a year.

When I grey out my vision starts to fade from the outside edges in and my hearing reduces. It’s as if someone is turning down the volume on both. This is the sign for me to find somewhere low and soft to either sit down and recover on, or to aim for if I black out completely. Sometimes I get white or silver spots shooting across my vision just after if I don’t black out completely.

When I black out I normally do not remember the grey out happening. I seem to lose about 5-10 secs of short term memory just before it occurs. If I was a disk drive I’d say the cache hadn’t been written before the power loss!

When I recover, my hearing is the first thing to return and all I can hear for a few seconds is the loud bass drumming of my heart. It’s like being stuck in a car with a teenager and his stereo, my entire body seems to vibrate with it. Then external sounds come back softly at first and then the volume is turned back upto normal levels. My vision comes back like an old style tv being turned on. It starts as a dot in the middle and spreads out in black and white before the colour comes back. Lastly I become aware of my body and whichever bit I managed to hurt when I hit the ground.

I’m normally a little clammy and fairly confused when this happens. However one odd thing I’ve noticed is that if I was drunk before, I come round feeling quite sober!

Two reasons I can think of:

  1. When you fainted, your vagus nerve was activated. One of the functions of the vagus is to cause sweating and we associate being sweaty with being hot.

  2. When you fainted, your body’s sympathetic nervous system temporarily shut down (or decreased markedly in activity). In the absence of sympathetic neural “tone”, your blood vessels dilate (that’s actually the main reason people faint with so-called vasovagal syncope). Dilated blood vessels (in the skin, at least) are one of the ways we respond when we’re too hot and need to dissipate heat from our body. In other words, we associate the ‘feeling’ of dilated blood vessels as being hot).

It’s also important to recognize that during the entire sequence, from “feel like I’m going to faint” to actually losing consciousness, there is a progression of symptoms. Early on, you sweat. But by the time you’ve passed out, that may have stopped and even though your blood vessels are dilated, your blood pressure and heart rate have both become so low that there’s not a lot of blood going to the skin. So, you look pale or ashen despite having your blood vessels dilated.