"Her teeth were chattering, she was obviously in what we call rigors [uncontrollable shivers]."
He added how he was scared that she was giving him "clues" when she said she was "tired" and so he wanted to keep the 63-year-old actress awake and talking.
He said: "I was afraid she wasn't going to wake up.
"Because you don't know if someone ... when they give you those clues, is she really now just tired, or is she going to become unconscious and this is it?
"So I wanted her talking ... that's how serious it was."
Her pulmonologist had originally rated her survival chances at 70 per cent but soon realised she was "in a bad way".
"It was all hands on deck.
"She had high fever, she was short of breath, very rapid heart rate, and a low oxygen level - which is not a good sign."
The Sister Act star admitted that she now realises just how "serious" pneumonia is and how she will no longer just "fight through" her illnesses for her ego's sake.
She said: "The crazy thing is people don't take this seriously.
"They don't take pneumonia seriously, and you have to.
"And this idea that we can fight through everything, 'cause that was my problem. I get a cold and I just ... I don't take stuff. I just fight through it. And you can't do that.
"It will kill you. Inactivity, not doing anything, not checking, will kill you. So get your ego together and say, 'Yeah, I'm going to the doctor because I don't feel good.'
"It's okay to go to the doctor because you don't feel good. Because you'd rather be alive b***hing about it than dead."
Whoopi admitted her health scare was a huge wake up call and she has cut back her hectic working schedule to look after herself properly.
She added: "I slowed it down because you don't want to relapse. I don't ever want to do this again.
"I didn't like it. This is what happens when you don't take care of yourself."