WASO (Wake after sleep onset)

Wake After Sleep Onset (WASO) is the total amount of time spent awake during the night after first sleep onset and before final morning awakening, summing all intra-sleep wake epochs. It is a core polysomnography and actigraphy metric standardised by the American Academy of Sleep Medicine. WASO contributes to the sleep efficiency calculation: SE = total sleep time / time in bed, where total sleep time = time in bed minus sleep-onset latency minus WASO. A WASO above approximately 30 minutes is generally considered clinically significant and is a diagnostic feature of insomnia disorder. WASO rises systematically with age - reflecting more frequent and longer arousals - and is elevated in obstructive sleep apnoea, restless legs syndrome, depression, menopause-related sleep complaints, and shift-work disorder.