After an upper-body workout—like curls or chest press—my upper back becomes stiff and I feel imbalanced while moving. One time, after a chest workout, I came home and lay on my back on the bed without a pillow, and I felt like the room was spinning. The spinning sensation went away after some time, but I still feel stiffness and imbalance while walking or standing. This only happens after a workout, and if I don’t work out, I feel fine.