There's one possibility in that you're experiencing a variant of sleep paralysis...

--> If your paralysis is hitting with your eyes closed, making it to where all you see is darkness, two things can happen. First, the darkness is left to be filled with imagery from your subconscious. Much of this (the space imagery and the reflective moon especially) relate to a gaining of some new perspective on things... a new view of the bigger picture. This can be especially scary and overwhelming if you were unprepared for it.

The aliens sounds like a carryover from the space theme, but taking the standard "trapped by a monster" reaction many people have to experiencing sleep paralysis....