Not sure but wouldn’t a heart attack wake up a sleeper?
No. There are such things as “silent” heart attacks with very little symptoms. There are heart attacks that feel like indigestion. Or pain in the jaw. Profuse clammy sweating, feelings of doom, dizziness, shortness of breath, may not be noticed in sleep either....
I guess that it is why the refrain in the child’s prayer goes like this, “and if I die before I wake....”