Approximately 20 to 60 percent of people with narcolepsy experience vivid hallucinations upon falling asleep (hypnagogic hallucinations) or just after awakening (hypnopompic hallucinations). These vivid hallucinations are often very scary. During the hallucinations, a person may be conscious but unable to move or speak even if the images are terrifying. After waking, it may take several minutes to readjust to reality and understand that the frightening or threatening situations were only hallucinations.
These episodes are not exactly nightmares—although people with narcolepsy, especially children, appear to be more prone to nightmares than others—but REM-stage dreams experienced when the person is semi-awake. Young children with narcolepsy find it especially difficult to separate these scary images from their everyday reality.
The presence of hallucinations, coupled with the fact that extreme fatigue is a symptom of other mental health disorders, sometimes leads people with narcolepsy to be misdiagnosed, which is why those experiencing symptoms are best seen by a neurologist or sleep specialist