Last year marked the toughest 365 days of Seattle Mariners right-hander Rob Whalen's life.

The 24-year-old pitched in just 12 games last season - 10 of them at Triple-A, where he posted a career-worst 6.58 ERA, plus another two appearances with the Mariners - and didn't pitch at all after July. But his struggles on the mound paled in comparison to what was happening off the field.

Whalen, who said he's battled depression and anxiety since he was a teenager, told MLB.com's Greg Johns on Thursday that he stepped away from baseball during the second half of last season in order to seek treatment for his illness.

"I was 23, I'd gotten to the big leagues and had a great life," Whalen said. "There wasn't a lot to be upset about, but I was just miserable. So it was hard to understand it myself, let alone explain it to others.

"I felt alone. I just isolated myself. ... I was fortunate enough to escape it."

Whalen explained that he showed up to last year's spring training out of shape due to his mental state at the time, and things only got worse for him during the season. The tipping point came during a Triple-A start in Reno on July 5 that ended up being his final appearance of 2017. Whalen allowed five runs in five innings during that game, and said that while he was pitching it felt like "the crowd (was) closing in on me."

"The start didn't go well, I felt like I couldn't breathe," he said. "I just packed my stuff and booked my flight. I was breaking down in my hotel room. I couldn't believe what I just did, but I had to do it."

Since stepping back from the mound last summer, Whalen has been seeing a counselor, something he's said has helped immensely. He claims to have dropped 20 pounds ahead of this year's camp, and said he's in better shape physically and mentally.

He also decided to use his platform as a big-league pitcher to make his mental health struggles public in the hopes that he can help others who are suffering but haven't been able to seek help.

"If I touch one person, it's a win for me," he said. "I'm not trying to get pity from anybody. It's my story, and I just want to share it and help somebody else.

"We need to change the stigma that you're fragile if you talk about it, because that's not the case. We need to continue the conversation."