Here is an interesting documentary from the series Ghost Visions which touches on the subjects of sleep paralysis, nocturnal assaults, somnambulism, sleep walking, possession and spirit release. The important thing is that it is open to the spirit hypothesis which is not discarded beforehand. It features experts on the subject like professors Allan Cheyne and David Hufford. It ends with a very peculiar case of spirit(?) harassment which is monitored by medical doctors within a hospital. It is certainly worth seeing.