This drug is a beta blocker. You can suffer serious rebound hypertension if you just stop taking it, especially at higher doses (100 mg) and if you have been taking it for a long time. You need to wean off this drug slowly. Cut your 100 mg in half and take 50 mg for a week or so. Then cut it down to 12.5 mg and take that for a week or so, before stopping altogether.
You can ask your pharmacist to just fill part of a prescription. When I was trying new meds, I would ask to just get 10 pills, so if I got bad reactions and couldn't take them, I wasn't out much.