Descent: Freespace.
The Shivans were creepy, that's certainly part of it, but I really think the problem was that the Lucifer became a metaphor for my own helplessness in my life. It was a bad time for me, constant fights with peers in school and no shortage of general troubles. I probably only narrowly avoided a felony assault conviction that year or the next.
And, of course, I couldn't leave. It was high school. You kinda have to get through that, more or less. Some people do okay without, but it's a rare circumstance.
The Lucifer bore a refinement on the Shivan shielding technology which was, to all human technology to date, impenetrable. You simply couldn't scratch the Lucifer. That ship became the scourge of the setting, carving a swath through the human and Vasudan territories.
As the gameplay takes place exclusively from the cockpit of a small fighter or bomber, it's no surprise that's where I found myself in dreaming. One night I dreamed I was escaping a massacre. My whole wing was lost, and my only refuge was a blind spot in the Lucifer's firing arcs: Inside the Lucifer itself, right into the fighter bay. I had a limited set of reference points, so it ended up closely resembling a Nebulon B Frigate from X-Wing. That's a blind spot for those, too, but parking even an A-Wing in there... Yeah, never mind.
So here I am, waiting in terror. If I try to leave again, the guns will take me down, or the fighter screen that's battling the last remnants of the fleet outside. If I stay, the Shivan fighters will eventually return and gun me down. I fire a few shots to see if I can take down the Lucifer from within, and discover the shielding is internal as well. I can even fly right through the round tunnels they use to get from point to point, an miraculously don't encounter any living Shivans, but the tunnels are just deadly habitrails for me. If I meet a Shivan, it can lase me to death. (They were nasty that way.) I even just start firing the guns as I fly through the tunnels, and nothing comes of it.
Helpless. Trapped. Hopeless, and soon to be dead.
Pretty nasty dream, really.