A 55-year-old man was admitted to the hospital in order to investigate an increasing number of incidences of a terrifying 'sudden intense bang or hit on the right side of the head, awakening him from sleep'. The episodes were occurring within an hour of falling asleep and without any obvious causal factor.
They lasted from a few seconds to several minutes about once a week for 12 years. They were described as being an unpleasant experience but not a scary one.
The patient was able to fall asleep within a few minutes after such episodes and to recall the experience in the morning. The awakenings did not cause daytime sleepiness.