No, that has not happen. Well not that I think of it it has. It may have been a glicth, or somewho I came off pause and died, because you didn't hear iut call for you when it awoke.
Something really similar has happened to 2 of my friends. It wasn't sleeping, but they both just paused theirs and unpaused it and it was there dead after being all healthy from before the paused it. I think it's a glitch. One of my friends thinks it's cuz her's was 99 lbs. I don't know, tho.