dead snail? floating

guess this is a dumb question...if a snail is floating is it dead? I have
had a handful of problems with this one snail...thought he was dead before
so I took him out and put him in a bowl did not see him do anything for a
couple days then one night my husband came home said he was climbing out of
the bowl so he put him back in the tank, then for the next few days he
seemed fine, now this morning he was on the side climbing now he is floating
across the top of the tank, now I know when I have dropped my other ones in
the tank they sink, so I am guessing floating is bad????
Nik