Can pain from a strain from lifting/pulling 50 pounds come and go? Bending over causes pain and then goes away. Walking on a treadmill, pain comes and goes. Pain is on the upper chest from shoulder to shoulder and in the back across the shoulders.
The pain first began moving a bale of hay, now with some physical activity the pain will come and last 5 or 10 minutes and go away. Don't get dizzy, don't get short of breath, heart beat doesn't seem to be affected.