Trying to contact us and why this way?

I am a light sleeper and wake at the slightest sound. On the occasion in case I woke for no reason at all and lay wondering what had awoken me.

I suddenly felt a pressure on my chest and a feeling that I was enclosed in darkness.

I could not move and the pressure got more and more and it felt like someone was sitting on me and trying to strangle me - cutting off my breathing. I was unable to push what ever it was off me - finally the pressure was released and the darkness left me.

What was it? Our mysterious visitor who leaves bad smells?

I have experienced the common feeling on waking that I have been paralysed - which is a sleep endused phenomenon and explainable - this was completely different as I was able to move my legs and arms but felt as if the pressure came from a person sitting astride my chest.