The 49-year-old actress - who filed for divorce from Ashton Kutcher, her husband of six years, in November, after he was accused of cheating on her - was rushed to hospital on Monday night and is said to be seeking professional help for the eating disorder after her weight plummeted in recent weeks.
An insider told RadarOnline.com: "She collapsed after having an epileptic seizure. Demi is in getting treated for anorexia, as well as other issues that caused her seizure.
"She has not taken care of her health at all lately and has lost a lot of weight."
After being taken to hospital earlier in the week, a representative for the 'Ghost' star claimed she was being treated for "exhaustion" and looking to improve her "overall health".
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A spokesperson for Demi said: "Because of the stresses in her life right now, Demi has chosen to seek professional assistance to treat her exhaustion and improve her overall health.
"She looks forward to getting well and is grateful for the support of her family and friends."
Demi recently admitted in the wake of her relationship with Ashton coming to an end, she has become scared she is "not worthy of being loved".
She said: "What scares me is that I'm going to ultimately find out at the end of my life that I'm really not lovable, that I'm not worthy of being loved.
"That there's something fundamentally wrong with me and that I wasn't wanted here in the first place."