"My back just kind of tightens up, and everything tightens around it," May said. "I have a spot in the lower back where it's a bit of a jabbing pain. It tightens because of the jabbing pain."
He is 2-2 with a 4.89 ERA in 43 appearances this year. His last appearance was Saturday, when he allowed a solo homer and two walks in Tampa Bay.
May admits he might have rushed his recovery a bit after his last DL stint and returned when the pain wasn't completely gone because he was anxious to play. When his back really flared up again, he decided he wanted to feel 100 percent and that he was willing to take the time away to get to that point.
"That's why I pulled the plug so quickly this time, because I felt like I wasn't me again," May said. "Right away, I knew what that was going to lead to. That wasn't fair to anybody on this team or myself. I wasn't going to wait for a four- or five-run blowup to say I'm hurt.
"It's twice as frustrating, too, because I felt like I'd figured some stuff out on the mound and things were starting to go better. I was honing in a little bit on what I needed to do, and I was feeling really good out there."
May, a former starter, had to make some mechanical adjustments in the bullpen after his increased velocity and the adrenaline from higher-leverage situations caused him to develop bad habits. He feels he didn't have the time to properly get himself into form for that new role, but is confident he can still do so moving forward.
"I feel like I can pitch in the bullpen again," May said. "I just made the changes and I was feeling really good and throwing really well for a month there. What I'm trying to do is avoid writing off being a bullpen guy because of my back injury. I think that I can pitch non-injured in the bullpen."
Chargois, 25, the No. 8 prospect in the Twins organization according to MLB Pipeline, combined to go 2-1 with a 1.35 ERA and 16 saves in 39 games with Double-A Chattanooga and Triple-A Rochester this year. He was the Twins' lone representative in the 2016 SiriusXM All-Star Futures Game in San Diego.
The hard-throwing right-hander made a brief stint with the Twins earlier this season, when he allowed five runs in two-thirds of an inning in a shaky Major League debut, a June 11 loss to the Red Sox.
"You're going to have your great outings, you're going to have your horrible outings," Chargois said. "I chalked it up as my horrible outing of the year and moved on. I owed it to myself and family and friends to get back here and do well. So that's what I'm trying to do."