I felt same thing doing weighted dips.Stopped the second I felt the twinge, turns out I tore my pec but it was a small tear in belly (not insertion thank fuck) of pec.
Got a few physio sessions and stopped training chest for 6 months. Got told my chest looked huge after
![Huh ???](http://www.getbig.com/boards/Smileys/classic/huh.gif)