Okay so I don’t know if I’ve been having these problems my entire life but I have started to notice them (either that or they started getting worse) at the age of about 13 , I was never able to sleep in the dark, there always had to be a certain amount of light where I’m sleeping if I’m alone for me to feel safe enough to sleep. 
Nothing has ever happened to me during the night to make me feel like something would.
I’m a teenager (in high school.) , my sister is able to sleep in darkness and I still can’t. There isn’t much of an age difference between us.
My situation now: sleep with 3 lights on, The light of the laundry room next to my room, the tv, and my LED lights.
While it does make me feel more comfortable while I’m awake especially if I’m the last one awake (which I hate, it’s terrifying) I still can’t sleep full nights or stay asleep.
I’m always look over my shoulder, or when I’m laying down I have to look up to check  over and over if I’m alone in the room since I always feel like somethings there. If I hear an Unexplainable noise, yeah there’s no way I’m sleeping that night.

Other than sleep, I’m not able to do presentations in online class anymore. I get way to scared and have to ask to do them after. When I’m home alone, (no matter how secure the house is) almost all the lights have to be on and a tv for me to feel safe, not entirely safe but it helps. If I’m home alone at night I’m constantly gonna be calling adults asking when they’ll be home because I always feel like something bad is always gonna happen.

And, big surprise, nothing ever does.