As I live in England, I am not that far from London. My mum's friend (a huge Harry Potter fan like myself) had brought us tickets to the Studio Tour and I was sleeping round her flat the night before we went. Her flat (or apartment) is about 2 years old therefore is relatively new, so the occurrences I am about to describe to you baffles me.
We had both gone to bed and for a while I read. After reading, I turned the lamp to its lower setting (its one of those touch lamps) and attempted to sleep. I heard a whispering in my ear - now if you have read my first story you will know that I have heard whisperings in my ear before. This frightened me as I couldn't tell what this voice was saying, it was just a muffled whisper right in my ear.
No sooner had I turned over when I heard a whistle at the end of my bed. I touched the lamp to it's full brightness when I suddenly heard two low growls next to me. I burst into tears and rang my mum.
The next morning I told my mum's friend about the night before and she was completely shocked. However, she did tell me that as she keeps a picture of her grandparents on either side of her bed, sometimes she will come into the spare bedroom and the skin sensitive lamps will be on, although no one but her had been in the flat. (She lives by herself.)
The only explanation I can think of for this happening is that I am increasingly becoming more sensitive to the spirit world, more so than when I was younger. I have slept around the flat many times before and nothing remotely close to that has ever happened.
How thick are the walls? What type of heating/air does it have? Does your mum's friend perhaps have new neighbors, since you last visited? These are all things to take into consideration before leaping to a paranormal conclusion.
Don't get me wrong, I'm not discounting your experience. I would have rung my mom too, or have gone to the living room couch, as I'm sure the bed would have been wet. And, YES, it is possible that you are becoming more sensitive. However, without some research, and perhaps spending another night there, it's impossible to say exactly what you did experience.