mrsmith--headaches vs migraines are largely different I believe in their intensity/duration and associated pain. Migraines are generally more severe (and can last longer) and are associated with sharp/stabbbing/throbbing pains, whereas headaches are more localized, less severe and more "pressure"-related.

As far as exercising, I echo what Mark said regarding getting a heart rate monitor. I've had one for a while now and it has definitely helped with my ability to ease myself back into working out and measuring my intensity levels. Start at an BP intensity level that you know will not induce symptoms and slowly progress from there to build up your tolerance. If your symptoms return or feel worst, take a couple of days off and try back at a lower level.

From everything I've experienced, if you are not pushing yourself at a sub-symptom threshold level to slowly increase that threshold/retrain your brain to take on more on a steadfast basis, you progression will be stunted.