Heidi has been estranged from Darlene Egelhoff since she unveiled her new surgically enhanced body to her mum earlier this year, showing off the 10 cosmetic procedures she had done within a 24-hour period.
But she was driven to tears by Egelhoff's reaction to her dramatic new look, claiming her mum studied her "like a circus freak".
She said, "She was looking at me almost like a zoo animal. It wasn't like I was her daughter anymore. She was looking at me like I was a circus freak.
"I tried to leave it as best as I could, but my heart was breaking."
On the latest episode of The Hills, which airs in America on Tuesday, Egelhoff says, "I haven't slept in months. I had to go get a prescription for sleeping pills just to be able to go to sleep at night to the point that I didn't even know how I would even make it another day.
"I've been mourning the loss of a child and, yeah, it hurts. It hurts more than I thought it could hurt."
The revelation comes weeks after Montag called the cops on her mum when she turned up unannounced at the home the star shared with her husband Spencer Pratt.Montag has since filed for divorce from Pratt."
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