Brie Bella does not hold back in the ring ... and she sure doesn't hold back when talking about a recent medical emergency that landed her in the hospital ... after she passed out on the toilet.

Speaking on "The Nikki & Brie Show" ... the WWE star and her sister Nikki Bella talked about her funny and terrifying episode when painkillers for her broken scapula left her severely constipated -- until the poop floodgates opened.

Long story short ... when she finally had a bowel movement, it was so much poop at once that she passed out on the toilet in her house.

Her husband called 911, and she was rushed to the hospital. On the ride there ... she noticed she didn't get everything in the toilet -- and there was still plenty of poop left in her pants.

And if the embarrassment wasn't bad enough ... Brie says she had to sit in her own crap for hours afterward ... because hospital staff needed to run tests and make sure she was properly hydrated before she could clean up.

They can all laugh about the situation now ... but at that time, Brie says that was some scary s***!