Mischa Barton is being held on a 5150 psychiatric hold, a source tells X17online.

The O.C. actress was loud and belligerent this morning around 7am at her LA home, walking around screaming in a fenced area on the side of her house. She was dressed in a white button-down shirt, her hair up but falling in her face, hanging over the fence that divides hers and her neighbor's yards.

We've seen video of the incident and at one point Barton yells, "Uh, bye ... like [laughing]. Anybody here? Oh my god, it's over. I feel it."

A neighbor tells X17online Misha was "pacing, screaming, getting into a shouting match with the neighbor, hanging over the fence ... falling off the fence."

We're told Barton was taken to Cedars-Sinai Medical Center in Beverly Hills for an evaluation that resulted in the 5150 hold.

Barton celebrated her 31st birthday with friends Wednesday evening.

In 2009, the actress suffered a breakdown for which resulted in her threatening to commit suicide, which led to her first 5150 hold. She was held at the UCLA psychiatric center for four days. She later said of the episode, "It was a full-on breakdown. It was terrifying. Straight out of Girl, Interrupted. Story of my life."