Hypomania can be a wonderful thing. If they could bottle it -- and make sure it didn't progress to full blown mania -- most of us would probably buy it. I would. When people are hypomanic, they can be outgoing, funny, confident, active, productive, focused. Anxiety seems to disappear. It really isn't a bad state in which to exist. The problem comes about if the hypomania crosses the line into mania. But really, a mild case of hypomania can be great.
Is the Celexa the only medication he's taking? Is he gaining weight? Does he eat all the time or only at certain times of the day?
by the way, it was 20 mg/day of Celexa over the course of a year that made my son psychotic, violent and attempt suicide. I'm not a fan.