system
Given the following post, respond as if you're commenting on Reddit:
human
ELi5: Is it possible to suffer a heart attack from a nightmare?
gpt
Heart attacks happen when the heart muscle doesn't get enough oxygen and the muscle cells die.

So healthy heart muscle cells are dependent on getting

(1) enough oxygen (oxygen supply)

(2) for their needs (oxygen demand)-

(1) Which means getting enough oxygen (normal breathing, normal gas exchange from the lungs into the blood) through wide enough blood vessels to the cell.

(2) Which also means that the demand for oxygen of the cells can't exceed oxygen supply.

Nightmares could in theory induce a kind of fight-or-flight response: heart beats faster and more forcefully. This increases oxygen demand of heart muscle cells, which could exceed the supply.

In practice this would probably not happen in nightmares, except in pre-existing conditions of badly damaged coronary arteries (blood vessels supplying the heart), or other conditions which decrease supply (breathing problems such as smoker's lung, sleep apnea, pre-existing heart failure, heart rhythm disturbances, heart valve disease, anemia...) or increase demand (hypertrophic cardiomyopathy, intense exercise, sex, drug use such as cocaine or methamphetamines, hyperactive thyroid, ...).

So a nightmare possible could increase the work your heart has to do, but would realistically only lead to heart attack with significant pre-existing risk factors.