The Heat star admits she was squirming in pain as her surgery approached and spent several days in hospital as her body "fell apart".
Brenneman refuses to go into details about what ailed her, but the 45 year old is relieved she's in recovery.
She tells website MomLogic.com, "It was as if my body knew that relief was in sight; that it didn't need to be a good camper anymore and hang on. Around January 15, it fell apart altogether and I found myself limping into the ER (emergency room).
"Everything went well. Of course it did - how could it not? I was with the top surgeon in the country for this sort of thing, at a major medical institution that did this kind of surgery all the time. I had sanitary surroundings, top-notch nursing and kind people constantly asking me if I was in pain - and if I was, doing something to rectify it.
"That said, the journey was not without drama. Because my body was failing, there were emergency situations, and I was in the emergency room three times in two weeks."
Brenneman admits she did a lot of thinking during her time in hospital: "When you're in physical distress, higher thoughts go out the window. Here I am - me, who loves thinking about God and art and politics and social justice; me, who is always looking for signs and portents and the Meaning Of Life - here are the kinds of thoughts I've had during the last month: 'I'm in pain. When am I not going to be in pain? I need to sleep. I need to eat. I'm cold. How can I get to the restroom with an IV and a catheter? And how the hell do the ties on a hospital gown work?'
"My world became very, very small. It reminded me of when my kids were newborns. Moment to moment - can't think beyond that. Eating, sleeping, pooping, crying. Elemental and animal. I was reduced to this.
"Perhaps by letting go of the search for the Meaning of Life, I stumbled into a piece of it, right there in hospital room 804."