Are There Other Explanations for Hallucinations?

There's one explanation for ghosts, but what else? One of the things that we're particularly interested in is a phenomenon called sleep paralysis. People can think that they're seeing kind of scary monstrous figures in the room. They can hear voices off footsteps and feel the pressure on the chest. It can be absolutely terrifying. Would not an unreasonable thing to think if you don't know about this thingcalled sleep paralysis.