my sixline has literally tried to kill itself twice. the first time it jumped out of my tank onto a glass cover i used to have right below my lights, was up there at least 15 minutes (i had just fed the tank earlier) before i heard him flop, was dry and stiff, i put him back in the water, he sunk to the bottom, and was swimming around within 5 minutes.
the second time was a few months later, i didn't see him for a few days, i happened to look at the rocks from underneath the tank (i was running barebottom) and i saw him wedged in a rock, after two more days stuck in there i took apart my rocks and freed him. he's doing fine now, active as ever, but i make sure i see it daily.
but i guess that doesn't compare to a firefish i had which disappeared one day. i opened my canister filter to clean it and found the firefish living in the top of the canister, and very skinny. it was in there for a month and a half.