Justin Bieber showed us his abs in this Instagram Thursday, Tweeting "Getting better," after collapsing on stage during his London concert.

Biebs' manager, Scooter Braun, took to the stage last night to explain to fans: "Justin got very light of breath. The whole show he's been complaining, and he's backstage with the EMTs and the doctor. They're telling him that they want him to go see somebody and see what's going on with his lungs."

The "Boyfriend" singer wrote, along with the pic, "Thanks for everyone pulling me thru tonight. best fans in the world. figuring out what happened. thanks for the love."

And just what was on Biebs' headphones, you might ask? Janis Joplin! The 21st century popstar was apparently listening to the 60's soul singer: "Gettin better listening to Janice [sic] Joplin," Justin wrote.

Even after passing out on stage, Bieber kept on tickin' -- his rep released this statement: "Justin fainted onstage tonight during his concert in London when he fell short of breath. He left the stage for 20 minutes, then came back and finished the show. He is now on his way to a doctor to get checked out and see what is wrong."

Maybe Bieber raised his blood pressure with his recent Twitter rant ... did that contribute?