I have a TWH that is very high-strung and he is 9 years old I might add. With him, lunging in circles does not help him to calm down...if anything it makes him more reved up. He will get to the point that he wants to stop, but its more because he's lazy...not because he is calming down. Plus the more you send them in circles, the better they get at it and the longer it will take. The best thing to do instead is ask your horse to go in partial circles and change directions often. That will force your horse to actually think instead of just run around mindlessly. I hope this helps you...cause I know exactly how you feel. Even if I take Major on a walk...I have to give him stuff to do (like go over obstacles, backup etc) because he is so hyper...I have to make him think.
Oh yeah...I also wanted to add that everyone is right about the sweet feed. With hyper horses like ours...it makes it 10 times worse. Major acts a lot better when he is just on pellets and hay.