Yes i'm on Concerta, which is for the ADHD i have, and it's a stimulant. I take 72 mg. of it. I don;t know whether it's that that's messing with my heart rate, or something else, but it'll take long to recover after exercise, it'll start racing sometimes when i'm sitting and a lot when i'm standing. Last night, i was leaning against the counter and i felt nauseous all of a sudden, short of breath, dizzy, and my heart was beating funny.