Every creature who has sanity has or know fear. It is just the question how big is this fear. In a normal dimension it let you be carefuller in dangerous situations and maybe saves your life. In an abnormal dimension you panic.
If you have no fear, you have got a big problem.
Probably you bring yourself and your friends in dangerous.
If ever there was a need to scare someone, I believe the answer is Dark Eldar Terrorfex or Horrorfex grenades, either one of those two should work since they're both designed to pretty much terrify the heck out of people with hallucinations.