Metoprolol can be discontinued quickly, but not usually unless there is something else going on and another medication is introduced to take over some of its function. At least, that has been my personal experience to date. I only ever ceased taking metoprolol once my first ablation had failed and I was in distress. The replacement was amiodarone to regulate my heart rate. I was told to cease metoprolol that very instant. No problems. However, the monograph for metoprolol usually says to not cease taking it abruptly, if I recall. I stopped taking it twice, and both times I took about a week to taper off.

I would let your physician know what happened. It couldn't hurt to experiment with cutting your pills into parts and trying to wean yourself off by reducing dosage by about 25% over a week...at least, in your case. Maybe two weeks just to make your heart notice the reduction less.