DENVER (CBS4)– A blood clot in the lung, called pulmonary embolism, is potentially deadly and much more common that most people realize.

Michelle Waller is an athlete who often goes for long runs as part of her training routine. She also climbs 14ers, snowboards on slopes around the world and mountain bikes with the best.

When Waller felt a cramp in her right leg it was no big deal.

“I could pinpoint the pain almost like a lump in my calf,” said Waller.

She continued training but one mile into a triathlon, “I felt like my lungs were going to collapse… almost like someone was sitting on my chest.”

Michelle Waller (credit: CBS)

Michelle Waller (credit: CBS)

Waller was treated for bronchitis but didn’t get any better. Later, a blood test revealed a problem and a CT scam showed it was serious.

“The doctor came in and he’s like, ‘You have dozens of clots in your lungs,'” said Waller.

Dr. Todd Bull is the head of the Pulmonary Embolism Clinic at the University of Colorado Hospital.

“Any more clots coming up there could have been life threatening or even fatal,” said Bull.

He said blood clots in Waller’s leg broke off and traveled to her lungs which blocked the flow of blood and strained her heart.

(credit: CBS)

(credit: CBS)

Bull said it’s not unusual, “It’s estimated that maybe 600,000 cases of pulmonary embolism in the U.S. each year.”

The condition can be caused by an injury, inactivity for a long time or estrogen in birth control pills.

“I feel very fortunate that I’m still here,” said Waller.

Waller was treated with medication. She has returned to competing but has learned to play it safe when it comes to her health.