Why does my roommate keep waking up in the middle of the night?

Okay so generally my roommate goes to bed around 12 but usually like less than an hour in or more she’ll suddenly wake up and sit straight up in bed like in a shock/panic? Like she gasps, usually sits there for a few seconds then lays back down and goes back to bed. She says she doesn’t usually remember doing it in the morning at all. One time she even shot straight up and jumped out of bed like she was freaking out. She did have a TBI a few years ago so maybe it stems from that? But it’s starting to happen more frequently and she says she’s never noticed of it happens when she’s home. I’ve never experienced anything like this before so i’ms just all foreign to me.