** Disclaimer: I'm not doc. I'm in a diagnostic medical profession and this is strictly just my opinion.**
Are you only having these symptoms when you bike or otherwise workout? If that's the case, they may not be getting a complete picture of what's happening to you. I would guide you towards a "stress test". This can be done at the hospital or at an outpatient facility. You go in, they put you on a treadmill, bike or other similar stressors and check out all kinds of things including your heart function. Of course it's more complicated than that, but you get the point. It could give a very good account of what may be ailing you. Also, there are a few different types of small, portable monitors that you can take with you for a few days. You do your normal routine (which for you includes biking) and it coughes out a full report. If you have an episode, make a note when/what you were doing and they will coordinate it with your monitor. Depending on where you live, there may be cardiac imaging modalities, non-invasive, that you can ask for.

Hope this helps. Good luck.
Cindy