The One Direction heart throb - who is claustrophobic - was panicking when he and some young fans were trapped in a lift in Milan.
He tweeted: "Eight of us got stuck in a tiny lift. Claustrophobia is a terrible thing, and people telling you to calm down is worse. I was freaking out. My heart is still thumping."
He was on his way to the lobby of his hotel with the elevator stopped and while it was said to be just for "five minutes," the singer's fear meant it became his "worst nightmare."
An insider told The Sun newspaper: "Getting stuck in a lift is Niall's worst nightmare and he started to get panicked.
"It lasted maybe five minutes, but once he got outside he was fine. But it felt like a lot longer than that to him."
The 'Story of My Life' hit maker has opened up about his claustrophobia in the past, particularly if he's surrounded by over-eager fans.
He has admitted: "I do get a bit scared sometimes - when we're in the tour bus, fans start climbing all over it and smacking on the windows, trying to get in.
"They start chasing after us, screaming. I'm claustrophobic and I don't like everyone crowding around and shouting questions. I get a bit scared."