F51 — Nonorganic sleep disorders

Concept, in one sentence

Nonorganic insomnia is a recurrent, impairing difficulty with sleep once an organic cause is excluded; sleep terrors (NREM, early night, no recall) and nightmares (REM, later night, vivid recall) are distinguished by stage, timing, and recall.

Decisive boundary cues

• Recurrent difficulty falling or staying asleep, daytime impact, organic cause excluded -> weighs toward F51.0.
• Early-night arousal, autonomic activation, no recall next morning -> weighs toward F51.4.
• Later-night vivid dream, well recalled, rapid full alertness on waking -> weighs toward F51.5.

Duration/course cue

Recurrence over time distinguishes a disorder from an isolated poor night or single bad dream.

Nearest alternatives

f53, f41

Common mistake

Treating any frightening night-time episode as a 'nightmare' without checking recall and timing, which can instead point to sleep terrors.

Retrieval prompt — one-line memory anchor

Is the episode recalled in vivid detail the next morning, or not recalled at all?