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It sounds like you just aren't used to being alone. The dark enhances that feeling. You were raised with sisters in your bedroom, so i think it can be normal for that reason.
I wouldn't worry too much about it if you're interested in having a partner in the future. Try turning off the tv and turn on a playlist of music (that will turn off after some time after you're guaranteed to be fallen asleep). And i dont see whats wrong with a lamp until you have a partner to sleep with in the future. Dont worry :)0