Non-24-hour sleep–wake disorder

Non-24-hour sleep–wake disorder (non-24), is one of several chronic circadian rhythm sleep disorders (CRSDs). It is defined as a "chronic steady pattern comprising [...] daily delays in sleep onset and wake times in an individual living in society." Symptoms result when the non-entrained (free-running) endogenous circadian rhythm drifts out of alignment with the light/dark cycle in nature.