Jansen explained Tuesday that he may be struggling due to the heart medication he was prescribed, and he has since decided to stop taking it after consulting with his cardiologist.
"I don't want to make excuses," Jansen said, according to Bill Plunkett of the Orange County Register. "But it's like you're sleepwalking out there. It makes your whole body go slow. I felt sleepy all the time."
The 30-year-old was originally expected to miss about a month after he was placed on the DL on Aug. 10 following an irregular heartbeat scare, but he returned much sooner than anticipated.
Upon being activated, the normally-dominant finisher has allowed four home runs in three appearances, all in the ninth inning and during crucial situations for the Dodgers. In 2017, Jansen allowed five home runs during the entire season.
He decided to stop taking the medication on Sunday after he got assurances from his cardiologist that it was safe for him to do so.
"I tried," Jansen said when asked about performing on the medication. "I thought the first day, maybe it would get better. Then the second day it was the same. And the third day …
"After that, I just thought, 'I'm going to hurt the team. I've got to say something and get off this medication.' It might be making sure my heart doesn't stop. But I told my doctor I can't pitch like this."
Jansen, who underwent heart surgery following the 2012 campaign, is expected to have a second operation following this season.