A desert snail can sleep for three years.
I feel like a snail spends most of its life playing dead. All it really ever does is sleep or remain very, very still. Snails need moisture to live, and as a result, they have developed many techniques for keeping their moisture intact. One development is that they are nocturnal. During the day, snails sleep in their shells, and during the night, they very slowly nourish themselves.
Desert snails can sense when the air is particularly dry, and will burrow underground in order to retain moisture. There, they can hibernate up to three years, waiting for the temperature to become more suitable for them. The average snail lives 15 very slow years.