I have been taking 12.5 mg of metoprolol every night since Decemb...

I have been taking 12.5 mg of metoprolol every night since December. I had no side effects whatsoever until here recently. One night I started getting heart palpitations and it lasted for 5 nights before I decided to try lowering my dosage. After I lowered it to 1/4 of a 25 mg pill, my palpitations at night got better, but I recently had a dizzy episode where my heart was beating at over 100 bpm. I have talked to my doctor and they are going to hook me up to a holtometer for a day on the 31st, but I don't want to wait that long since my heart beat has been increasing over the days on 1/4 a pill and half a pill makes me have palpitations at night. So I was wondering, if my doctor has me change medication, does anyone here know about any good meds that do the same thing as metoprolol?