I'm sure you just imagined it. If you'd had a heart attack
, you'd know, believe me. You'd have experienced a piercing pain in your chest and be short of breath
What likely happened is you were in a relaxed state and you became aware of your heart rate
slowing down, then you either fell asleep or fainted. I can assure you, your heart didn't stop.
Might be wise to get checked out at the Doc's anyway, to see if there's any reason for that fainting
spell. You might have low blood pressure.