I've been having dreams that I can't tell if they're just memories. Like, it's normal stuff that cold actually happen in real life. Which is disturbing in and of itself

I've always considered any dream that upsets, scares, or unsettles me to be a nightmare. Google defines it as "a frightening or unpleasant dream", which I think is in line with that. Not all bad dreams have to be intense, traumatic events but they can be, especially if they are centered around traumatic memories or repeat/happen enough to warrant concern. Most of my nightmares happen just once but usually they freak me out enough that I need to sit up in bed for a while with a light on because I'm scared to go back to sleep or am still trying to process the feelings the dream gave me. Even though the body is shut down during sleep, the mind definitely isn't and the emotions you feel in your dreams absolutely effect your waking self, too