Sömndjup

Sömndjup is a Swedish term used to describe the depth or quality of sleep. The word combines sömn (sleep) and djup (depth) and is common in everyday language and popular science. In clinical contexts, the term is informal; sleep depth is usually described in terms of sleep stages rather than a single measure.

In sleep research, true sleep depth corresponds mainly to slow-wave sleep, or non-REM stage 3 (N3). This stage features delta-dominant EEG activity, reduced autonomic arousal, and diminished sensory responsiveness. Deep sleep occurs primarily in the first sleep cycles and is linked to restorative processes and memory consolidation, though overall sleep quality depends on multiple factors.

Subjective sömndjup refers to waking ease and freshness after sleep. Objective assessment uses polysomnography to determine sleep stages; wearables estimate depth indirectly via physiological signals. People can report different perceptions of sleep depth than what is measured, illustrating a gap between subjective experience and objective data.

Factors influencing sömndjup include age, circadian phase, sleep pressure, caffeine or alcohol, medications, and sleep disorders such as insomnia or sleep apnea. Sleep restriction can increase deep sleep pressure temporarily, while aging generally reduces the share of deep sleep. Individual variation is common.

Thus, sömndjup is a colloquial way to discuss how deeply one sleeps, closely tied to slow-wave sleep and overall sleep architecture.