Bret Michaels -- Tour Turns Into Bloody Mess ... In and Out of 6 Hospitals

Bret Michaels is in the hospital again, after a series of serious medical emergencies during his tour.

The Poison lead singer postponed a concert in Champaign, IL last week so he could undergo kidney surgery to correct a problem triggered by his diabetes.

He sucked it up and made his Friday date in Memphis and Saturday's show in Knoxville ... but things got ugly quick.

The stents started bleeding out while he was on his tour bus ... forcing him back to the ER where stents were removed.

This isn't the first time Bret's diabetes have acted up on tour ... he was rushed off stage for a similar problem back in May after performing just 3 songs.

We're told Bret's been admitted to 6 different hospitals over the last 2 weeks -- yet he didn't cancel a single show.

Now that's something to believe in.