TMI, Jen!

Jennifer Lawrence was a guest on "The Late Show with David Letterman" on Wednesday night, where she revealed why she's been feeling so under the weather lately ... in great detail.

"I thought I had an ulcer," she told Dave. "I just had this really bad pain for like 3 weeks. You can only s**t your pants so many times a day before you have to go to the emergency room, where you're like 'I need to go to the hospital.'"

The outspoken 23-year-old actress then described getting an endoscopy to find out what was wrong.

After getting put to sleep, J-Law recalls dreaming "there was a nuclear bomb," before waking up and having a conversation with her doctors about the Kardashians.

Earlier in the evening, she hit the red carpet for the final premiere of "The Hunger Games: Catching Fire" in NYC -- where she reportedly told the press she was feeling good, but "gassy."

We can't get enough of Jennifer's press tour moments, she's always good for a laugh!

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