Hibernation

The Silurians and Sea Devils went into hibernation after detecting a rogue planet on a course for Earth. (TV: Doctor Who and the Silurians, The Sea Devils)

Sorvix automatically went into hibernation when they were sick whilst Mystics deliberately did so to find God. The Fallen Tyrant of Taladel was kept in a cocoon for 4,000 years before he was woken up and killed. (AUDIO: Aliens & Sex & Chips & Gravy)