Like 99fairies said, probably paranoia.

It doesn't have to be psychosis, though. Things like OCD can cause paranoia (for example). So it could be anything, really.

My personal opinion: there's a difference between animals/aliens vs thinking the Russian mafia has a hit on you. Technically speaking, an animal tearing you apart is possible (even though highly, highly unlikely), but the Russian mafia hit on you? Not realistic at all.

The alien thing imo is tough to say. It could be a fear stemming from childhood that's resurfacing; in which case, it's not necessarily psychosis. (I'm just presenting a counter argument. It could very possibly be psychosis instead.) But I'm not a dr either. Maybe you can ask a dr what they think?