This condition is called sleep paralysis and is very common sleep disorder.
The same experience happened to me for the couple of times in one period of my life, years ago and never came back.
It was while trying to fall asleep, with the same feeling of awareness of surrounding and extreme pressure on my body that was paralyzing me. The most intensive pressure was felt on my throat. I was getting the feeling that I am not alone and I was extremely frighten.
I can relate this appearance with lack of sleep and extreme mental and physical exhaustion.
Try to recognize what is triggering this?
Do you have a regular healthy sleep pattern?
Avoid stressing to much.
How old are you? I had this experience when I was 15 or 16 years old.
Waiting for your post!
Best wishes!
Marija