But what initially started as a feeling of uneasiness eventually turned into a serious three-day trip to the hospital and a procedure to remove an ulcer from his body.
The unexpected illness that landed Collmenter on the 15-day disabled list on Aug. 10 began when the D-backs flew home from a trip in Pittsburgh.
"I just felt sick," he said. "I never experienced anything like it before. There was no warning. It just came out of nowhere."
When the 26-year-old returned to his home, he spit up blood and became worried. That's when he knew a hospital trip was imminent.
Doctors ended up finding the ulcer with a tube and cauterizing it. The procedure forced Collmenter to rest up for three days before returning home.
Now a week later, the pitcher is returning to baseball activities. He threw a bullpen session on Saturday and is scheduled to throw an inning at Salt River Fields on Tuesday.
"I took a little time off, then I started throwing last week and now I'm feeling like myself again," he said. "I was weak when it first happened, but now I feel good."
On the season in nine starts and 13 relief outings, Collmenter is 3-3 with a 4.24 ERA and 69 strikeouts.