A Murphy bed cannot kill you.
I have been pushed up into a Murphy bed as a kid by my brother as a prank one night and nothing bad happened to me.
I did freak out though because I was not strong enough to get the Murphy bed to go back down but I did not get hurt.
Murphy beds could likely kill a baby or small child if it were to go up on them but that does not usually happen.
Most Murphy Beds stay down on their own until you physically lift them back up into place.
Other than my brother pushing the Murphy Bed up on me I've never had a Murphy Bed fold up on it's own.
Murphy Beds are pretty safe and also are great for small apartments or when you need an extra bed but don't have the room for one.