Rousey says she was on the losing end of the fight as early as the first round. She was eventually taken down by a kick to the head, and the match was called after 59 seconds in round two.
"I cut my lip open and knocked a couple of my teeth loose [in the first round.] I was out on my feet from the very beginning," Rousey explains. "I wasn't thinking clearly. ... It was like a dumbed-down dreamy version of yourself making decisions. ... I was just trying to shake myself out of it. I kept saying to myself, 'You're OK, keep fighting. You're OK, keep fighting.'"
After her disappointing loss, she and her boyfriend, fellow UFC fighter Travis Browne, drove 15 hours to a remote ranch in Texas.
"I kind of just slept a lot and ate fast food," she recalls. "First I was so sick I couldn't eat anything. Then I just slept and pooped in the woods. I used a whole roll of toilet paper in one day. Physically, my body was refusing its own failures. It was, like, sick of itself. Expelling itself. Like all the skin came off my face. My whole body flushed it out."
".... I'm just really f**king sad," Rousey comments.
Rousey reveals she shut herself off from the world to avoid what was being written about her, but she does respond to the criticism she got -- interestingly enough, even from Lady Gaga -- for not touching gloves with Holm before the fight.
"It was just like a reaction," Rousey explains about giving the cold shoulder to Holm. "I was like, 'The last time I saw you [at the weigh-in], you were putting your fist on my chin and trying to get a cheap hit on me, then you turn around and you want to touch gloves? You have to be one way or the other. So if you want to be that way with me, that's the way it is.'"
But it wasn't all negativity from fellow celebs. Rousey reveals that tennis champion Serena Williams reached out to her after Thanksgiving, and the two met up for a sushi dinner in Los Angeles.
"I f**king love her," Rousey says. "Everybody else is like, 'Oh, I'm small and proper and tennis-y' and she's just like, f**kin' muscles, curvaceousness, awesomeness. She doesn't back down from anyone."
Now, Rousey wants to come back stronger than ever, though she's still physically hurting. Last week, UFC president Dana White confirmed that she will indeed get a rematch against Holm.
"Of course. What else am I going to f**king do?" she says when asked if she plans to fight again. "I need to come back. I need to beat this chick. Who knows if I'm going to pop my teeth out or break my jaw or rip my lip open. I have to f**king do it."
ET caught up with Rousey in September, when she was in much higher spirits talking about getting a shout-out from Beyonce during the singer's concert in October. Beyonce played Rousey's viral speech on not being a "Do Nothing B**ch" for the crowd.
"To be honest, it's an honor to have a real powerhouse of a woman like Beyoncé just recognize my existence," Rousey told ET exclusively. "It's surreal how something I thought was a pre-fight rant in my hotel room that would end up scrapped on some editor's floor has taken off to the point a cultural icon like Beyoncé is playing it between songs at her concert. Such a huge compliment, I couldn't be more grateful."