I had a cichlid in a 10 gal. tank when I was first getting started. He was a healthy guy but not always well cared for, I would forget to change his water, overfed him all the things that should have killed him. This went on for about 2 years.
When I moved into this house (during the summer), I was worried I would lose him & his tank mates, so I got 2 cheap styrofoam coolers, filled them half way with water and put him in one and the rest of the fish in the other. Something happen, it may have been the beer, and I totally forgot about him. Everyone else made it into the tank that night and was fine. A WEEK later I looked into this cooler and there he was in about an inch of water!! I got him into the tank and 3 years later he finally died.