supraventricular tachycardia
"I have had PSVT and occasional atrial fibrillation (plus the related anxiety from these conditions) since I was 21.  I am now 44.  I have been on metoprolol 25 mg, once a day in the morning, for the past 18 months and I love it. I was originally put on it twice a day, but I already had bradycardia and low blood pressure at night so within a couple of days the nighttime dose was making me wake up gasping for air with an extremely low heart rate and blood pressure so low it wouldn't register on my home monitor.  I called the doctor and he said to not take the bedtime dose. I haven't had any side effects that I recall. On the contrary, I can now play sports with my kids without flipping into an irregular rhythm."