The 23-year-old singer said he used to force a smile during many performances as he struggled to cope with the band's success.
"I shouldn't have been able to do as many shows as we did, if I'm honest about it, if I'm brutally honest about it," Payne told The Sun.
"Going out and putting that happy smile on my face and singing the songs, honestly, sometimes it was like putting on one of those costumes, going out there and, underneath the costume, people don't really see what's going on," he added.
"I let it get to me that day. I wasn't in a good place. And unfortunately I was going through a rough time and I let it get to me a little bit too much. That was it," he said.
"The more we did, I just don't think we stopped and celebrated enough how great things were and I think that's what got on top of us in the end," he added.