Normally, yes you don’t move in your sleep…actually can’t. BUT there are circumstances that allow you to This site has more information on night terrors and such I have had experiances where my ex-fiance has litterally had to hold me down to keep me from hurting myself by acting out a dream. So there are instances where your spouse or partner would know for sure if you were having a nightmare
I’ve had dreams where I fell from a tall building and hit the ground, and I’m still alive. Not often, but once or twice. The bit about “If you don’t wake up before you hit the ground in your dream, you die for real” is a plot device for stories, not grounded in actual medical fact.
There is a dexamethasone suppression test. It is complicated to explain, but if positive, & assuming no serious physical problems, it is very specific -95% accurate -to diagnose bi-polar disorder.(manic-depressive), & those folks are frequently paranoid. BTW, of all people who die in their sleep, it is not from a nitemare (but how do we know?) & is most likely to occur from about 3AM-5AM. I recall being taught this, but have no cite.