Is it normal i notice this about crossing my arms

There's a reason for that but I forgot it. My uncle and cousin do it too I was told.

Interesting!

It's probably to do with the way it makes you breathe. My guess is that it slightly restricts the movement of your rib cage and lungs. This could make you feel a little anxious in your sleep as well as making your breath more shallow thereby allowing less oxygen to reach your brain.
People who go on holiday in the mountains often experience different kind of dreams due to the change in the altitude and air quality. They say it gives you weird dreams as well.

I think you are wrapping yourself up and protecting yourself.
Those dreams are just dreams, as the years go on, you actually want more new ones.