Hi RC, I was diagnosed with Sinus Bradycardia in August 2005. I spent the spring and summer before my dx feeling pretty terrible. Very low energy, flu like symptoms basically I just felt like crap. One day I got up to get ready for work and just passed out on the floor. I was sent to the ER where my heart rate was in the 20's. I really had no idea. After spending two weeks in the hospital, trying multiple medications to try to keep my HR up the ending result was a pacemaker. I was 31 years old at the time.
The facts are that Sinus Bradycardia can be lived with when your HR is in the 50's & 60's. But eventually it can start to drop to a point where your symptomaic such as dizzyness and being lightheaded. This is all because your heart is not pumping enough blood/oxygen to your brain. Then the passing out can start as your body will want to get you supine inorder to get the blood to your brain. This is really scary.
Make sure you talk to your doctor about how your feeling. See what your options are and please do keep us posted on how your doing and how your appointment went. Take care