Surely not! Restarting a fishes heart by tapping on its stomach?
You can stun fish for a short period of time, they do it at fishing lakes to check stock, the fish float to the surface and appear dead, they check them out for infection, and then just leave them, they revive themselves a short time later. Maybe the heater plays up in this tank and this fish keeps bumping it, and it gives that fish a small electric shock?