Poor Justin Bieber! He works so hard to deliver to his loyal Beliebers that he actually made himself sick. The Canadian superstar actually vomited onstage last night (Sept. 29) in Glendale, Ariz. at the opening date of his long-awaited Believe tour. Warning: Do not watch this video if you have a weak stomach!

During his performance of 'Out of Town Girl,' Bieber suddenly stopped singing. You almost couldn't tell that he stopped singing at first because he was crooning along to a backing track -- which isn't something that should surprise anyone, given the intricate choreography that goes into all of his shows. However, you can sense something is wrong when the 'Believe' singer turned around suddenly and hunched over, holding his abdomen -- and something is very wrong, as he begins to puke all over the stage. Yikes!

Bieber later attributed his illness to first-night nerves and combining too much milk with his rigorous dancing.