What Causes Excessive Laughter While On Treatment For Bipolar Disease?

My brother laughs uncontrollably, whether the TV, Video is on or off. Even when lying in bed in the dark, no sounds other than him. This has been going on for the last 5*6 days. He s almost 21 and just came out to California from Chicago. He s been living with me about 2 weeks. He is very angry with his parents, and was on an anticonvulsant for Bi-Polar treatment about a three weeks before he came to California. He threw his remaining pills away after he found out he was coming to CA for sure. He is ADAMANT that nothing is wrong with him. Should I be concerned?