Frankie Muniz's Secret Health Battle: How He Survived a Racing Accident and Is Fighting Mysterious Mini Strokes

In 2009, Muniz had a serious accident on the race track

He’s proving himself to be a solid competitor on Dancing with the Stars, but Frankie Muniz is still adjusting to the occupational hazards of his new gig.

“I’m using muscles that I’ve never used before,” says Muniz, 31. “The backs of my knees are sore! Every day there are new pains, but I can’t stop.”

And for the former star of TV’s Malcolm in the Middle, some physical aches and ailments are nothing new. The actor, who left Hollywood in 2006 to become a professional race-car driver, admits that he can be somewhat injury-prone.

“Since 2006, I’ve broken 38 bones,” says Muniz, who has also endured nine concussions since the age of 7. “As a kid I did everything. I played ice hockey, soccer, basketball, soccer. But a year ago I went roller skating, and I was literally the dad holding onto the rail. I realized I have to take care of myself.”

In 2009, Muniz had a serious accident on the race track: “My car flipped a bunch and I crashed into a wall. In the end, I broke my back, ankle, four ribs and my hand. My thumb was dangling by the skin.”

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During his recuperation, Muniz began drumming in the band Kingsfoil and found a new passion for music.

“I loved the band, I loved the guys, I loved every aspect of it,” he says. Muniz also managed the band and by 2014, he was ready for a change.

“From the time I was 8 years old, I never stopped working,” says the former child star. “In 20 years, I had maybe 30 vacation days. I realized I was exhausted. It was good in the sense that I could literally do whatever I wanted to. But bad in the sense that I don’t know how to operate when I don’t have to be somewhere.”

Muniz was also living with a puzzling condition. In 2012, he suffered his first mini-stroke, or transient ischemic attack, during which blood supply to the brain is temporarily cut off. (Unlike a stroke, there are no lasting effects). Since then, Muniz estimates he has had 15 mini-strokes, varying in frequency and length.

“First, I lose my peripheral vision,” explains Muniz of the attacks. “And I can see people but I can’t recognize them. I can see words but I can’t tell what they say. Then I start going numb. It’s a gross feeling. But I know now when it’s going to come. I usually go lay down and wait [for it to be over].”

“I’ve gone to so many neurologists who have done every single test,” he says. “I have no answers as to why it happens. I got so tired of trying to find an answer that I don’t think I’ll search for an answer anymore. I’ve accepted it.”

PEOPLE’s special issue 25 Seasons of ‘Dancing with the Stars’ is on stands now.

The actor —who is excited about a return to Hollywood and happily dating his girlfriend of a year and a half, Paige Price — believes staying positive is more important than dwelling on the past.

“I’m a little more easygoing now,” Muniz says. “I’m in a good place. I smile more.”

He dances more, too.

“Everything I’ve done up until this point is exactly what I’ve wanted to do and I’m happy,” he says. “Even doing Dancing with the Stars. It’s perfect! And I love it.”

For more on Muniz, pick up the latest issue of PEOPLE on newsstands Friday.