I actually had an alien nightmare last night after watching Aliens. It was vague.
I was in a parking lot in front of a strip mall. It was the dead of night and no one was there. Even though it was abandoned, there were cars lining the parking spaces. I walked up the road to the last parking space and looked into the window of a store from across the road. Inside there were shadows just moving... They looked like aliens. They just crawled around and knocked stuff over. I got scared and ducked behind a car. I started moving in between car after car, trying to get far away from the store. Then I heard glass break, and weird scratching noises. I waited behind the car for a long time, really scared. Nothing happend for the longest time, so I looked over the car. The window from the store I looked in was broken. The aliens were gone, except for one. It looked back at me and I ducked under the car again to avoid its gaze. I continued crouching from car to car so I wasn't seen. Then I heard a very loud shriek go off behind me and I looked over to see the head of an alien peer around the side of the car and hiss. Then it left, for some reason it didn't see me. I got up and ran down the street, I have no idea why, dreams are weird. I kept running, but it was more like a jog. Suddenly I wasn't in the parking lot anymore. I was across the road from it on a sidewalk. A forest was off to my side. I heard glass breaking to my left and shrieks. So I do something I would never do IRL, I run into the dark forest. As I crunch through the leaves at a slow walking pace, a loud siren goes off from the road. (Like the one in The Mist) Those scare the shit out of me, so I freeze. Then I hear a slow crunching behind me, it gets faster and faster, until I turn around. And when I do, I wake up.
It was strange how I just jogged or walked at times, while I was terrified. I remember thinking "run!" But my body wouldn't respond. I didn't actually see much of the alien, just in the store and the head. I assume one killed me at the end of my dream, but I'll never know. It was very eerie.