Trivia: When it's severed, Anton's hand is portrayed by the hand of actor and magician Christopher Hart. If that name is familiar, it's because Hart actually briefly made a career of playing disembodied hands. He played "Thing" in the 1991's "The Addams Family," "Addams Family Values" and "Addams Family Reunion." He played Anton's severed hand in this film. Then he played two animated severed hands in the television show "Angel," in the episode "I Fall to Pieces." He has an... oddly specific career.
Trivia: When the hand is killed and Mick complains about how there was "no explosions of hellfire," this is actually an inside joke. The original ending was completely different, and involved a giant portal, explosions, hellfire and tons of effects. However, this ending was dropped because the filmmakers felt it too scary compared to the rest of the movie. A new, more comedic ending was then shot. Mick complaining about the hand's simple death is a reference to the original, more intricate ending.
Trivia: The film's release was greatly impacted by the Columbine tragedy. It was unfortunately scheduled to come out only 10 days after the shooting, and as a result many theaters refused to screen it due to it involving teens and violence. Additionally, several politicians (unfairly) criticized the film immediately after the shooting, earning it a lot of bad publicity. The studio quietly canceled the premiere and dumped it in theaters, where it bombed. It later found a cult audience on home video.
Answer: He was either too high, sleepwalking or under the evil hand's control.