"I lived probably 10 years in a really, really deep depression," the Kennett, Mo., native, 34, tells PEOPLE Country. "Growing up in a small town, it was one of those things that you don't talk about and you try to sweep it under the rug."
Newly married when "Let It Rain" hit No. 1 (he wed wife Catherine in 2009), Nail appeared to be living his dream. But, he says, "I carried around a lot of guilt because I had all these blessings in my life and yet I was still struggling to try to find some joy. I'd be first to admit that I wasn't always the easiest guy to be around."
In 2012, Nail "bottomed out," he says. "But I finally realized I didn't have to do this on my own. I'm a singer, not a doctor. I decided it was time to seek out help so I made some changes and leaned on other people rather than trying to figure it out all by myself, which is what I had done for years."
Through therapy and prescription drugs, Nail has embraced a more positive attitude – and found a way to create more upbeat music with his new album, I'm a Fire.
"In the few months leading up to the record, I found an inner peace and good place that I hadn't seen in a long, long time," he says. "As a result of that, the music began to feel how I felt personally. It's brighter, it's bigger, it has more tempo. The lyrics are more positive than in records past."
Nail's new outlook seems to be working: His album's first single "Whatever She's Got" hit No. 1 and became his first single to sell a million copies. "Right now," the singer says, "things are marvelous!"
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