It happens to me too!!!! I know it's the same because it's what I felt when I was running in the Navy. Infact, the lifting gets my whole system going so much, I have trouble sleeping. I'm on this huge high and I'm sooooo awake. Within a half hour I want to lift again (eventhough my muscles are sore). I don't as I'm afraid I'll injure something....but it's amazing what weights can do for you! I"m really happy I included this in my diet plan. It's been several years since I've lifted anything (except kids)....I think it's the best thing I could've possibly done for myself!!