When someone dies of an heart attack in their sleep, why was that the point when their heart failed? Their heart should be at a minimal level of exertion. The person is lying down, relaxed, with low heart rate. That seems like their heart would not be under any stress at that time. Why didn’t the fatal heart issue manifest itself earlier in the day when the heart was under more exertion? It seems really weird that the person can spend the whole day moving, walking, in stressful situations, etc. and the heart is fine, but then they lie down and relax and their heart fails.
I don’t know that heart attacks are that tightly linked to stress- I suppose the plaque or whatever could just dislodge and clog up the works at any time, stress or not.
While you await a definitive answer, here’s a personal observation. A few years ago I was having episodes of severe chest pain at night that would awaken me from sleep. Because I didn’t die, I assumed I was experiencing episodes of GERD, and I took an antacid.
The episodes became worse and more frequent. Turns out I was experiencing unstable angina and at least one of the episodes caused damage to my heart muscle (a “heart attack”).
I had a stent placed and have been fine. I wondered why the events happened at night, never during the day. Maybe some hypoxia during sleep?
I don’t have a source other than My Father the Doctor (on whom be peace), but when I asked him much the same question his response was that the failure often occurs when the victim is starting to wake up — in other words, when the heart switches modes. A rough analogy is an incandescent light bulb, which frequently burns out right when it’s switched on.
To be taken with a bushel basket of salt, unless and until confirmed by a genuine physician.
IDK, but here is a perhaps relevant anecdote. In 2007, my pulse had dropped to the low 30s and I was put on something called a Halter device, essentially a 24 hour cardiogram. When I went back to hospital to have it removed, the technician said my cardiologist would get the report in a couple weeks. I then walked a half hour to my office and by the time I got there the technician had reviewed the tapes, noted a 7 second period with no heartbeat during sleep, called the cardiologist, who called my wife, who called me to schedule a pacemaker, which was installed a day or so later. She may have saved my life, for all I know. Perhaps a 7 second gap could have become a 7 minute gap and then poof.
I’d heard of research that implicates a large amount of dietary heme, from hemoglobin, in night-time heart attacks in people already predisposed to heart attack.
So, yeah, that big rare steak, possibly washed down with plenty of red wine, just before bed … that’s a bad idea. I save that for lunchtime. 
LiveScience ref: Too Much Iron from Meat May Raise Heart Risks | Live Science
Another WAG, while awaiting a scientist, is that some of the night-time heart attacks are caused by or exacerbated by sleep apnea.
During sleep, even normal sleep, there can be peaks of adrenaline in the bloodstream. Adrenaline not only ‘stresses’ the heart, but makes the blood more likely to clot (with a clot in one of the arteries going to heart being the immediate cause of a heart attack).
Surges of adrenalin are more prominent when people snore and especially if they have sleep apnea (stop breathing from time to time during sleep). Presumably this is because the blood oxygen drops when you stop breathing (or can’t breath) and that signals the body to release adrenaline into the blood. Adrenaline and its cousin noradrenaline when released cause the heart to speed up, the blood pressure to rise, the blood to be more likely to clot, the coronary arteries to constrict, and the heart muscle’s electrical system more likely to go into an abnormal or even lethal rhythm.
You’ve never had a dream that caused stress? or anxiety?
Sure I can believe that there might be moments in a dream or whatever where someone’s heart rate might rise, but it doesn’t seem like it would be all that different from earlier in the day when they were moving around, going up stairs, doing laundry, etc. It seems weird that someone can spend all day doing normal activity and then at some point in the middle of the night it’s too much for their heart.
But it sounds like there are some heart attacks which don’t necessarily have anything to do with high levels of stress or exertion. Maybe some clot breaks off or some heart tissue has a random malfunction and interrupts things enough to interfere with the heart.
So then, is it possible that the heart being in a very relaxed state would actually make some heart attacks more likely? That might be how your car can drive fine on the highway but will stall at a red light. When you’re up and moving about, your heart is going more at full speed and minor issues have less of an impact. But when your heart is relaxed and beating slow, those minor issues might have more of an effect.
I heard an answer to this a while ago, that part of the process of waking up is a surge of adrenalin to get the person “started”. This extra stress is what brings on a heart attack. As opposed, I suppose, to dying quietly in your sleep (as the joke goes “…like my grandfather, not screaming and yelling like the passengers in his car.”) where whatever was going to do you in happens during the period of rest.
My dumb thoughts would tell me that someones brain is still in the works…
you having all this thoughts running in yo head even when you sleeping…others might be or can be so disturbing…bad dreams and staff…your heart if weak at times can not handle such…i have woken up a few times due to a bad dream and felt my heartache a little.
I wouldn’t be surprised if a lot of heart attacks while sleeping are people with undiagnosed or untreated sleep apnea.
Also, WAG, but if your sinus rhythm is slow, it may be interrupted by a supraventricular impulse, leading to ventricular fibrillation and peaceful death?
(Not a cardiologist)
Pay attention, folks. This info is from the SDMB’s very own Academic Internist, Who Knows Medical Stuff Like That.
So glad you came back, KG!
Heart attacks and other cardiovascular events are not more common during sleep, they actually peak shortly after waking. We don’t know why.
People are asleep for 6-8 hours. It could be just…time.
I’ve heard/read that shortly after waking has to do with changes in rhythm, physical activity, and even habits such as brushing teeth, which may cause inflammation. I would imagine, however, that the factors are as individualized as the person who sustains the myocardial infarction.
Is that also why old people can have heart attacks when startled or frightened? Rather than a high heartrate causing something to break, instead these hormones are bringing about quick changes in the heart that cause the heart attack?
How dangerous are those pranks where people wake someone from a deep sleep by scaring them with loud noises or whatever? I guess if you’re young your circulatory system is strong enough to take the sudden change, but it seems like it could also have deadly outcomes.