Ask an Eye Doctor and Get an Answer ASAP
Do you see double? Do you have any other medical conditions? What medications do you take? Do you have any neurologic problems, like numbness or weakness in your legs or arms?
It sounds like your eyes are not working together. When you look to one side or the other, one eye leads and the other lags. That is probably what is causing the symptoms. Thyroid disease is one thing that notoriously can cause this. Another condition is a neuromuscular disease called myasthenia gravis. Finally, together with the "swollen optic nerve" and numbness in left arm, I would get a scan to look for signs of MS as well. I am glad you are seeing an eye doctor (make sure its an ophthalmologist) because these are some serious conditions to rule out.
Hope this helps and good luck.