In an upcoming MTV documentary set to air November 30th, Britney talks about her very public meltdown, saying, "I sit there and I'll look back and I'm like: I'm a smart person. What the hell was I thinking?" Referring to her divorce from KEVIN FEDERLINE and her custody battle for her two sons, Britney says, "I've been through a lot in the past two or three years, and there's a lot that people don't know."

As far as an explanation for her behavior, Britney says, "Sometimes I think I get kind of lonely because you don't open the gate up that much, you know I mean? You're guarded. You have to be that way, so I'm kind of stuck in this place and it's like: How do you deal? And you just cope, and that's what I do. I just cope with it, every day."

The documentary, tentatively titled For The Record, will air two days before the release of her new CD, Circus. Britney's new video for "Womanizer" will premiere tonight on ABC's 20/20.