I've had a total of three lucid dreams within the last year. All three of them are always the same. I'm also a bit embarrassed posting this but I am starting to feel a bit wierded out about it. So here it goes: I'm having sex with an invisible person. There is a feeling of someone on top of me and holding me down. I'm not scared during this and I find it pleasurable. Although yesterday, I went to bed with the intention of having one of these again. I was aware I was sleeping, but thought I might be awake at the same time. I then felt a presence on the bed and it felt like someone was sitting on my right arm, something very heavy. I didn't panic and finally the sensation of being held down went away. I then continued to have the usual sex dream with this invisible person.
note: These always happen during an afternoon nap.
Before posting this, I did do a forum search on this topic and the only thing I could find similar was something called 'old hag'.