I've progressed up to 480mg of Verapamil over time and I've never felt a lack of energy exactly, but I have felt light-headed often when first moving to a higher dosage. I have a fitbit with a heart rate monitor and I could tie this to a low heart rate -- in the 50's and sometimes even in the upper 40's. As Dr. Geske told me (and I had already figured it out) the impairment of HCM on the heart's functioning varies depending on eating, alcohol, heat, exertion, stress, caffeine, etc. and I found that when I lost 15 pounds I needed to go back to my lower dosage because I was light headed all the time. You might try checking your heart rate and blood pressure to see if the feeling ties with abnormally low heart rate/blood pressure. I've added Norpace to my regimen and am going through this myself...we backed of the Verapamil because I was feeling a little overdone.