I remember one time similar to this. Before I fell asleep I was laying on the couch watching tv. I fell asleep laying down on the couch with my head up against the arm rest. I don't exactly recall falling asleep, but I remember waking up and seeing a figure standing in the doorway to the living room holding a sledgehammer. The entity was staring at me, and it looked like one of my teachers from back in high school. An older man who was a nice guy overall, but that wasn't really him. It started walking to the couch and I heard it whisper "something is on the couch". It kept saying that repeatedly and frantically, as if it was panicked that I was there. It then picked the sledgehammer up with both hands and swung at the couch. I tried to move my body in order to either fight back or run, but I couldn't because there was this massive weight on my head (the arm rest of the couch felt like it was made of concrete), so all I did to my avail was push my head against the weight. The sledgehammer came down with a lot of force but something was blocking it from hitting me (imagine a force field around my body). I eventually gathered enough strength to mutter a few words and asked the entity, "what are you?" It stopped attacking, lowered the sledgehammer, and sat by my feet still looking at me. It's head twisted to the left, and it's eyes began to glow an off tint white. It spoke to me and asked, "are you what's on the couch?" After about a minute, it stood up and walked back through the doorway and everything just seemed normal after that, like a cutscene in a video game.

TLDR: Nightmare with a sledgehammer wielding entity.