That sounds really hard (improbable) to do. I've done all sorts of nasty things to my limbs in Morpheus's realm but never pulled a pec. I have, however. often managed to sleep face-down with my fists in the middle of my chest and then breathing is tough for a while.

Is this an asymmetric pain? One side much more than the other or just over on the side? If central and of more than a day's duration I'd go see the Doc!