A Death Trance is a trance that only children of Hades (and possibly also Pluto) can enter. The person must eat one of Persephone's pomegranate seeds in order to enter the Trance. One seed is equal to one day, during which a person who entered the Trance lies in a deathlike hibernation and consumes no oxygen. It is unknown whether or not the user ages during the trance.
When captured by the Giants Otis and Ephialtes and trapped in a sealed bronze jar, Nico di Angelo enters this trance to stop himself from using up all his oxygen. When Percy, Jason and Piper free him, he is said to be extremely weak and malnourished.