Credit: Jason LaVeris/FilmMagic

Demi's darkest hour.

Demi Moore turns 50 this November -- and it appears the Margin Call actress, on the heels of her devastating split from Ashton Kutcher, is now suffering a full-blown mid-life crisis.

After weeks of hard-core partying at various spots around Hollywood, it all came to a head on Monday evening, when the painfully skinny star called 911, was rushed to a hospital, and explained through her rep that she's seeking "professional assistance to treat her exhaustion and improve her overall health."

An insider confirms to Us Weekly that Moore suffered a seizure on Monday, prompting her 911 call. (TMZ claims that Moore was doing "whip-its," inhaling nitrous oxide, to get high.)

"She has spiraled," the source explains, "and gotten to a place where she is struggling too much to function."

She announced her split from Kutcher, 33, in November, following his September affair (on their sixth wedding anniversary) with 22-year-old Sara Leal.

"Her life is completely in crisis," continues the source. "She is turning 50 and has no idea who she is or what her focus should be."