ICYMI ... Gayle did the big reveal on "CBS Mornings" Tuesday as she explained in graphic detail why O was missing a scheduled book club segment because she was down bad with a stomach bug. GK let the world know her bestie had stuff coming "out of both ends."

Welp, lots of people thought Gayle did Oprah dirty by exposing that much nitty gritty about Oprah's illness -- but Wednesday morning, Gayle made it clear the dynamic duo's as tight as ever by posting a video call they had discussing the aftermath.

She defended herself, saying ... "The only point I was trying to make is to show how badly you wanted to be there to promote the book -- 'cuz you never miss those ... It had to be something that would keep [you] from getting on a plane and coming."

Oprah supported that sentiment, and definitely was not angry about Gayle's description. She did confirm she landed in the emergency room to get treatment for dehydration, and was too weak to fly.

She did say 5 people in her household caught the virus, which she said is highly contagious, and she encouraged everyone to wash those hands!!!

One other bit of fallout from all of this ... Oprah says her phone and inbox were blowing up -- not unlike her GI tract -- with people reaching out to make sure she's okay.