I really should have read that back before posting. Sorry.
I think you can figure most of it out. The tube pulled off the needle leaving the needle in my arm. My own little bloodgun. Squirted about 5 or 6 feet when the spray was not blocked by intervening white uniforms.
Frankd6, lancing the boil on my scrotum with the Exacto-blade didn’t hurt all that much. But what made me howl was when I put rubbing alcohol on the wound. 
JoltSucker: I have never personally anyone pass out when the tourniquet is released after taking the blood sample
due to sudden changes in bld volume or bld pressure but since I’m not your physician my answer is the most likely explanation. Anything is possible so perhaps there is another explanation. There are several other physicians on the SDMB who may want to offer an answer your question
I’ll answer the easy question first. For-pay donation centers do not use the blood products for transfusion into human patients.
Even in the late 1970’s pre-AIDS era, this was true.
In college, I solved the “work & have no time to party; don’t work & have no money to party” dilemma by selling plasma twice a week. Got $20/week for 2 donations; Dale got the same - life was good. 
But, none of the plasma went into patients. It was sold to lab companies who pooled thousands of units of it & sold it to be used by medical laboratories as controls. (make sure that the instruments & reagents are working properly), and sold off to research compnies. But because we were paid for donating, it couldn’ be used for patient donations.
The harder question is explaining all the weird reactions you all describe. I can’t. Wasn’t there; didn’t observe it; can’t really add anything to the conjectures already posted. This is why we doctors have a fancy intimidating word “idiopathic”; it sounds better than “I have no clue”… Even better is “idiosyncratic” which means it’s the patients fault for not behaving according to our expectations.
Laura, it sounds as though, for whatever reason, you had a massive “vagal” reaction - surges of nerve activity through the parasympathetic nerves which causes slowed, heartbeat, low blood pressure & involuntary urination and/or defecation. Labelling it as such doesn’t explain why it happened, though.
Sue from El Paso
Siamese Attack Puppet - Texas
Experience is what you get when you didn’t get what you wanted.
Most of the theoretical causes listed would cause only short-lived symptoms, though. I am weak and sick for the rest of the day after giving whole blood, and fine after giving plasma or platelets.
Jill
Sue, I’ve got another name for it here in Denver.
“OOTT syndrome”
(OOTT= one of those things)
Works in absence of easy explanations for those things that …well, just happen.
GB
When I give blood, I feel like I’m going to crack up laughing. I have to bite my lip until it almost bleeds to keep from doing it.
Must be a mild light-headedness thing.
“You should tell the truth, expose the lies and live in the moment.” - Bill Hicks
I give blood every two months and i think i know the answer to your question…
every body reacts differently to losing blood. Your body has only 8 pints in the system and often times the body will go into shock because its about to lose a pint. the faintness comes from not getting enough blood into the brain (probably the pint intended to go to the brain, is quickly filling up in a bag :)). Another problem is that your body is nervous and adrenaline is kicking in… hope i’ve helped you!
The first time I donated, I had no adverse reaction at all. 'Samatter of fact, I had my daughter with me, and she fell asleep on my shoulder while I sat and donated.
The second time, though, I had a similar reaction to Ruffian. Things were just ducky until I had finished, then I was sitting there and wondering why on earth the nurses were asking me if things were all right. Actually, they seemed to be yelling at me from very far away. Everything fuzzed out, and I’m told that my fainting was the hit of the day. Glad that my daughter was at day care that time!
Waste
Flick Lives!
you shouldn’t eat a big meal but you should definitely eat. you need some sort of nutrients in your system because so much proteins leave the body in the blood.
“Life is too short and too long to be unhappy.”
Sue: Yeah, I figured the answer was somewhere along the lines of “I know what happened, but I don’t know why.” The body is such a complex thing…who knows what exactly causes what. I’m ultimately chalking it up to shock, figuring my body freaked out at the loss of blood–even though I personally didn’t mind the needles, the blood, the whatever. Nervous? Not at all–notsomuch a tremble or an anxious thought. I was much more interested in the article I was reading (and am still bummed I didn’t get to finish it).
I think a few hundred years ago I would’ve been the type “doctors” of that day would have said had “weak blood.” I am extremely prone to motion sickness, pass out/puke/all variety of fun things when menstruating (mercifully spared now that I’m on the Pill), grow dizzy and disoriented when my allergies are severe and my sinus are inflamed, and am prone to fainting at higher altitudes (only other time I passed out was after hiking at a high altitude and getting sick). I do tend to have low blood pressure, so that probably factors in, somewhere.
Side note: I recently had bloodwork done for my yearly physical. The girl before me was truly phobic of needles–I heard her nervously wailing, then sobbing, then outright shrieking when the needle was inserted–top of her lungs, “Oh my God I’m going to die” screaming. I heard the nurse tell her, “If you move, it will hurt more!” This girl (late teens-early 20s) was seriously hysterical. Of course, I was the lucky one to go after her. I was fine, and actually talked with the nurse a little about her experiences.
I can’t believe someone can be that freaked out about a little needle. But of course, I’m terrified of heights. What do I know?
Teaching: The ultimate birth control method.
I’m not a doctor, but again, doesn’t this point to lowered blood pressure as the cause? My normal blood pressure is 90/60. Taking any out seems like it would lower it further.
But I could be way off here. Sue?
Jill
Jill,
Blood pressure is mediated by a variety of factors,
Minute by minute adjustments are made by heartrate and vascular constriction/dilation.
Hormones mediate kidney function and thirst to retain or exrete water, this is a much slower process.
Then there are “abnormal” effects. Severe allergic reactions can cause anaphalactic shock; bee sting reactions are an example. This causes all the blood vessels to dilate, the pipes get bigger, and the pressure of the liquid in the system drops.
Blood loss and dehydration lead to hypovolemic shock, which is low volume, and I won’t even get into cardiogenic shock in todays lecture.
One of the confusing points is that although the cause is different, many of the symptoms are the same.
People reasonably assume that blood loss would be the cause of low blood pressue symptoms after donating, and that may be right, however the volume given is usually well tolerated in the healthy adult, that’s why the chose it. OTOH I would be hard pressed to tell the difference between an allergy shock, and volume shock or an anxiety shock without a history or labs to guide me.
the point is that an idiopathic reaction similar to an allergy, or anxiety, or a vagal response like Sue suggested could account for most if not all of the symptoms described above. Frankly, without a detailed work-up it’s doubtful that anyone could explain the exact reason for Ruffians reaction.
Afar as you go, it depends on why your BP is 90/60. If you are a young, skinny, athletic 90/60 with a heatrate of 55 (athletic bradycardia), you can probably tolerate a blood donation just fine, your heart rate will go up to 85 until you replace the volume, water will do, and your aerobic capacity will be decreased until you replace the red blood cells. If you’re 60 years old, 70 pounds overweight, and your BP’s 90/60 because of a small heart attack you had last year, they probably won’t let you give blood.
Clear as mud? I guess that’s why it’s taking longer than we thought 