The bespectacled star had to film party scenes while he was chronically sick and he swore off the local cuisine once he started feeling better - so he would be healthy for the rest of the shoot.
He tells Entertainment Weekly magazine, "I got very skittish. All I ate were peanut butter and jelly sandwiches. That was all I trusted."
And Helms' co-stars could not believe he was still functioning while he was so sick - because, when the cameras weren't rolling, he was curled up in the foetal position - in agony.
Bradley Cooper recalls, "We had to shoot this scene one night where he had to be shirtless, going crazy in the street, with tons of extras. It was unbelievable. He was literally in the foetal position in the back of some bar and then he would get called to the set, stumble out, start dancing and screaming, and when they said, 'Cut,' he'd go right back into a foetal position.
"Zach (Galifianakis) and I just kept looking at each other saying, 'How is he doing this?'"