Any new meds? Many have the side effect of lowering BP, possibly heartrate, and some can also inhibit epinephrine/adrenaline, so you're not getting your normal boost of that during exercise.

Both consult your doctor, and wikipedia, as I've found that sometimes doctors can leave out mentioning a critical side-effect. I do both, and never start a new drug without researching it myself. In one case long in the past before I did my own research, I suffered a severe side effect which I later found out is common and the doctor never mentioned it. In a more recent case, the doctor recommended a med on their last visit with me, they were leaving, I researched first, and there were huge red flags such as highly addictive, never use as first course treatment, and if needed, use only for limited time. I mentioned this to the new doctor and they were like, "Uh... that was bad advice."