Tired of being made fun of it by the PT and other patients, thinking of putting something in front of my mouth to muffle the sound (but it makes breathing from the mouth a bit harder/can't relax the arms/upper body as well if I do this which helps me to relax in general)

There are specific scream muffling products but they often contain a small rod part of some sort which won't work so well for the stretch where I am on my belly face down