Nightmare that I can never remember but makes me wake up absolutely terrified

I sometimes have nightmares, which is pretty normal, sometimes they are mild and rarely they are so intense that I wake up screaming. Well that is how it used to be for as long as I remember. For the last year or so, I'm experiencing something different. From time to time I wake up at night, screaming and acting like I'm fighting with something. The strange thing is I pretty much never recall these events, I learnt about those from my mother who is sometimes awoken because of my screaming and she told me about it. I don't remember the panic moments, only that I'm in bed awake feeling like something just happened, but I don't recall what exactly.

I must admit that what creeps me out is what I often shout in those situations (again, I don't remember doing this). I shout things like "Get away from me!" "This thing is here, stay away from me!".
The whole concept of "this things" freaks me out. I don't believe in demons and other-dimensional beings etc but I'm not a skeptic either. If this is just a product of my subconsciousness, where did it come from and how do I get rid of it? I know there are both believers and skeptics on this forum, and I'd really like to find out what both groups have to say about this.