First time was when I was 20. There's a really interesting story behind that one but I'll talk about my second experience instead.
I was about 22, working in a foreign land, renting a small room with a queen bed stuck between two walls where I slept on the edge, facing the wall.
I woke up in the middle of the night, unable to move. I was on my left. Brain is completely clear but my body was not listening to me.
I took deep breaths to calm myself.. I told myself I had experienced this before, and all I needed to do was wait. I'd get muscle control back.
And then I felt someone breathe close to my ear. I froze, and the hairs stood up on my back. I barely had time to react when I felt something.. a person.. lie down behind me and adjust themselves. You know how you can feel that because the mattress shakes, moves and depresses? Yeah. That.
My mind raced. I was like, on one part of my mind just repeating "this is just an illusion" and on the other it felt so real, it was unmistakable that someone or something made its way onto the bed and was lying behind me. I tried to move and couldn't.
As my fear grew, I started panicking. And then I found myself angry, angry that I was afraid. I was like, spirit or ghost, I will fucking face you!!! What can I lose?!!! HUHHHH and then in my anger I wanted to twist my whole body to confront whatever was behind me, and my body listened, I did turn, and nothing was behind me.
I slept with my back pasted to the wall.