History: I have been on a beta blocker for rapid heart rate since 2004: 2.5 mg Bystolic once a day. Current: for the past Week and a half this is what I am experiencing - Anytime I get up to go/do anything, my heart rate escalates to between 97-130 quickly and as soon as I stop/sit down, it decreases rapidly to my normal resting rate of between 53-60. This causes dizziness and extreme fatigue. What could be the problem? Please advise what to do and potential causes.