My mother once told me something that happened to her on holiday, (both my parents died quite a while ago now).
Anyway, she and my Dad were on holiday in a caravan park. In the middle of the night, Mum woke up and needed the loo. She didn't want to wake my Dad so she didn't turn the light on, just made her way across the caravan in the dark.
She was just about to reach the door of the loo when a dark figure, about six foot tall, loomed up in front of her. She could tell it was a man by the shape and size, but the figure was like a solid black shadow in the darkness, she couldn't make out any details.
She naturally assumed that it was my Dad, thinking that he'd gotten up before her to use the loo himself and she didn't realise. So she said, "Hello, I didn't know you were awake?" (or something similar.)
In the little bit of light that came in through the gap in the curtains she could see his teeth suddenly gleam white in a huge grin, but she still couldn't see anything else about him except total darkness.
At which moment my Dad's voice came from behind her, "What?" and she realised that he was still in bed,.
Totally startled Mum turned to look towards the bed, and when she turned back the grinning shadow was no longer there.
Probably a half-awake/half-dreaming incident, (but she swore she was totally awake and there was something sinister there) (She was a bit annoyed when I suggested it might have been the spirit of Ross from "Friends")