I have one little guy that is doing the same thing.He has been eating well although not as plump as the others and seems to struggle as he moves about the tank.This morning i noticed he was gone and saw him laying under a pile of java moss i though he had died but the little sucker popped right back up and went bask to his bopping around the tank.I am hopping i get get some meat on his bones and give him a good life..