Today for the first time I took Beta nox rather then my normal caffine (coffee) and I felt good at first but about 1/4 the way through my workout my pump was great but I felt so sluggish and every set made my heart race like crazy. My heart kept skipping which I never get. I have great health and i see a cardiologist every year. Has anybody had problems with this stuff ?? Now Im 10 times more burned out then normal for post workout.