Am 7st8 an every time i lay on my sides to try sleeping my chest goes all tight and feel like i can't breath properly it's pretty scary?

Relaxation: It would be reassuring if you have no breathing or other respiratory problems lying on your back or when you're up and about walking, climbing stairs,doing housework,etc. The uncomfortable sensation you experience when lying on your sides would then be a matter of tension in the rib cage but not a serious issue of a cardiopulmonary problem.