While i was bench pressing i felt my shoulder slide back but i have all the symptoms for shoulder impingement syndrome is?

May be instability: Impingement usually occurs with shoulder press or military press. You may have experienced shoulder instability. Impingement typically occurs in older patients (>35 or 40) while instability occurs in younger patients (< 30.) initial treatment for instablity involves a physical therapy program. Impingement is treated with nsaids, physical therapy, and steroid injections.

Unstable Shoulder: Posterior shoulder injury is one of the most commonly missed diagnoses. Your description sounds like you suffered an episode of posterior subluxation. Remember impingement is a non specific term that really isn't an anatomic diagnosis. Impingement can result from rotator cuff weakness from muscular inhibition secondary to instability so its important to get the right diagnosis. http://www.thesh.