These aren't common side effects of atenolol, which include, but aren't limited to: Tiredness,
low blood pressure (hypotension), slow heart rate, cold extremities, dizziness upon standing,
depression, nausea, dreaming. They are, however, most likely, symptoms of being hyper again, since you aren't on anything to help control your Graves Disease.
I understand that 10 mg methimazole was too much and caused you to become hypo, but was there some reason you aren't willing to be a reduced dosage, such as 5 mg?
Some Graves Ophthalmology is irreversible; it's not a good idea to irritate it further if this can be avoided.
When will you be having your thyroidectomy?