I slept on the couch and woke up with left arm pain. i have pain and difficulty in lifting my arm over my head, taking it behind my back and moving my forearm outward. what should i do?

Sat night palsy: That's due to a temporary nerve injury (aka saturday night palsy) from sleeping in an awkward position (usually with your arm raised and compressed under your head. It will resolve in several hours. If not, it may be a spinal or joint problem which needs to be looked at by your doctor.

Shoulder: This is rotator cuff tendonitis. Another possible issue is cervical disc/radiculopathy.

Slept on arm: You probably had your arm go to sleep because you were laying on it (blocking normal blood flow). Usually the symptoms go away within the first 20 min or so after you wake up. Sometimes a bruised feeling might persist for a day or two. If your symptoms are worse than a bruised feeling you should seek a medical evaluation to make sure something more serious is not going on.