Armond,
I've been using EFT, almost daily for the last 4-5 months. I'm not a practioner but have studied the first two sets of DVD's and read an enormous amount of information from the emofree.com newsletters and other sources. I do not believe EFT can bring about any negative side effects. The nervousness/anxiety you mentioned were likely independent of the tapping you had done but brought about by something else. Maybe related to the bipolar disorder, or just the normal stress of living in this crazy world. Who knows! With EFT, you don't always have to figure out the why, just tap for the symptoms you're feeling at the time. (EX: Even though I have this nervous feeling creeping up on me and I'm not sure what's causing it, I love myself deeply and accept myself fully. Even though I'm anxious and it's causing my heart to pound, I love myself deeply..... etc.) I can't say EFT has worked for me every single time I've used it, but it has worked amazingly well on many occasions. Gary Craig emphasizes to "try it on everything" and "don't give up if it doesn't work right away, BE PERSISTENT!" so that's the advice I would stress to any EFT newbie. Best wishes!