She is 6 mths old, been in her own room for a few weeks never had a problem. The past week shes woke up hysterically screaming without stirring before about 2 hours after going to bed. She sucks a few oz (no dummy), then goes back to sleep. So I don't think shes hungry because she would stir first. I thought it could be teething but I have given calpol before bed, and used teething gel and like I said she goes straight back to sleep most of the time. Sometimes it is her teeth but that keeps her awake. The only other thing I can think of is she's hitting her head on the cot bars when shes moving in her sleep and rolling, but I'm scared to use cot bumpers so i don't know how I could make it comfier. Either that or DP has said a ghost 
I know seperation anxiety can peek at 6mth but she happily goes back to sleep after a quick cuddle and a drink, so i'm stuck for solutions as sometimes it happens just as i fall asleep so i feel exhausted.