Insanity Rules
Insanity
A dimension where none of our physics work, called "a dimension of pure chaos", wrecks havoc with the human body—especially brain chemistry—at a quantum level. No wonder people go completely insane—imagine having your entire body infused with drugs, made from your own chemistry and more. It doesn't quite explain the more supernatural stuff, but crewmembers going berserk and attacking each other? Real-life drugs have had that effect, and altering brain chemistry itself, if not outright killing you, would make you less than human.
They will see and hear things that are not there, and will ignore obvious stimuli that contradict the "reality" of their hallucination. Damage taken from these hallucinations will seem real to the character, and is quite capable of causing death if the damage is severe enough. Psychosomatic shock from the event can throw the victim into cardiac arrest or even cause the manifestation of some physical trauma at the point of the "injury". The GM should make full use of hallucinating PCs early in the adventure, especially while they are unaware that they are hallucinating. This is the perfect time for a character to hear voices in the distance; see a dark figure standing in a doorway; catch the glimpse of a dead body rising from the deck; or see a gaunt-faced man in a mirror. A careful GM can milk these hallucinations for a long time, keeping the PCs unaware of the truth and - more importantly - frightening the daylights out of them.
Eventually the players will begin to realize their fears are only illusory.