postural orthostatic tachycardia syndrome
"Didn't seem to lower my heart rate very much, except when I tried to walk around in physical therapy class.  Then it caused a severe drop in my heart rate, from about 95 in the relaxed sitting position, to below the 50s when I walked a few yards.  Bradycardia is a documented side effect, and unfortunately one I suffered from.  Also had lots of goosebumps, tingling scalp, chills and flushing throughout the day.  I'm not totally knocking it, because I know it works for some POTS patients, but it wasn't the medicine for me."