Deep sleep (slow-wave sleep)

Deep sleep, or slow-wave sleep (N3), is the stage characterised by high-amplitude delta waves on EEG and the highest arousal threshold. It dominates the first third of the night and drives growth hormone release, cardiovascular recovery, immune regulation, and glymphatic clearance of metabolic waste. Deep sleep declines with age, and lower amounts are associated with poorer memory and increased risk of neurodegenerative disease.