Benign Sleep Phenomena

Benign Sleep Phenomena includes sleep paralysis, hypnagogic hallucinations, hypnopompic hallucinations, and hypnagogic jerks. In isolation, these are occurrences are benign and not pathological.

Hypnagogic hallucinations are vivid perceptual experiences occurring at sleep onset, while hypnopompic hallucinations are similar experiences that occur at awakening.^[1] These experiences own their own are not symptoms of a pathologic illness. However, the presence of other signs and symptoms such as cataplexy and sleep paralysis may be suggestive of narcolepsy. Hypnopompic hallucinations may be a better indicator of narcolepsy than hypnagogic hallucinations.

The prevalence of hypnagogic and hypnopompic hallucinations in the general population is uncertain. However, it occurs in up to 30% of patients with narcolepsy.^[2]

Sleep paralysis is a temporary inability to move or speak while waking up or falling asleep. Episodes usually last for a few seconds or minutes. Sleep paralysis itself is not harmful, but can be very frightening for patients.

Hypnagogic (Hypnic) jerks (also known as sleep starts) are a sensation of “falling,” “shock,” or “falling into a void” accompanied by non-periodic myoclonic movements that usually involves isolated body segments.^[3] They are associated with autonomic activation with transient tachycardia, tachypnea, and motor activity. The causes of hypnagogic jerks are unknown. Theories for their origins include descending volleys within the pyramidal tracts at the transition from wakefulness to sleep. Sleep starts are common physiological phenomenon affecting up to 70% of the adult population and their course is benign, resolving without any neurological sequel.

• NHS: Sleep Paralysis