When I began to learn Taichi, I had the same experience. It's a brand new thing for me. I was a little nervous and excited, so I couldn't sleep very well. Later I felt ache in my knees, thighs, legs, back and waist which made me wake up at midnight.Now seven months passed, Taichi has worked on me. All my friends have asked me the reason why I looks so good, the healthy skin, more energetic. My teacher told me the longer you play Taichi the more benefit you take from it. That's true. I really believe it. Now I have had good sleep everyday. So I suppose the "extra energy" is probably from your mind at the beginning of the playing Taichi. That's natural. You'll be fine after days playing.