Kamikaze Fish

I came back from a weekend away, and went to feed my fish. He's normally at the top wiggling around desperate for food even if he's just been fed. He wasn't in the tank though, and in shock I looked around and found him on the floor looking very dead! I picked him up and he gulped, so I put him back in the tank and helped him recouperate. Luckily he seems fine now, but I have a plate on the top of the tank now! I'd be gutted if he died, as I've had him for over ten years. The other, larger one died a year ago or so, but he was absolutely massive, and couldn't really see anymore.