Christina Applegate's Daughter Diagnosed With Debilitating Disease Amid Her Multiple Sclerosis Battle

Christina Applegate is facing another health battle in the family after her 13-year-old daughter, Sadie Grace LeNoble, was diagnosed with POTS -- postural orthostatic tachycardia syndrome.

On Tuesday's episode of Applegate's "MeSsy" podcast with Jamie-Lynn Sigler, the "Married... with Children" star's daughter joined them to talk about her own health challenges and what it's like to be a child of someone with multiple sclerosis.

"I have something called POTS. I have no clue what it actually is, but it has something to do with the autonomic nervous system, and it affects my heart," Sadie shared.

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"When I stand up, I get really, really dizzy, and my legs get really weak, and I feel like I'm going to pass out."

Sadie also recounted a time in school when people thought she was just faking her condition "to get out of class."

"In class, if I were to stand up then, I would be like, 'I have to go to the nurse. I can't do this.' Or I'll be in PE, and I'll be like, 'I have to go to the nurse.' They were like, 'You're doing this to get out of class. It's probably just anxiety. Go back to class.' They wouldn't do anything for it," she recalled.

"Them not doing anything about it definitely hurt me physically and emotionally. Because I was just like, 'This is rude, and I feel sick, and you're telling me to go to PE and run laps around the football field. I can't do that.'"

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POTS is "a condition that causes a number of symptoms when you transition from lying down to standing up, such as a fast heart rate, dizziness and fatigue," according to the Cleveland Clinic.

While this condition is not life-threatening, it can significantly interfere with one's day-to-day tasks as its symptoms include dizziness or lightheadedness when standing up or prolonged standing in one position, fainting, forgetfulness and brain fog, heart palpitations, exhaustion or fatigue, nervousness and anxiety, shakiness, shortness of breath, feeling sick and headaches, among many others.

Knowing how POTS affects her child, Christina, who is battling multiple sclerosis, told Sadie, "I hate it for you my darling. I really hate it for you. I'm sad. But I love you and I know you're going to be OK. And I'm here for you and I believe you. And thank you for bringing this to light and awareness."

Meanwhile, talking about her battle with MS, her daughter said, "It was hard seeing my mom lose a lot of the abilities she used to have in my childhood... It's definitely hard seeing my mom struggle with this."

She added that being diagnosed with POTS helped her better understand what her mom is going through.

"Like, when my mom's like, 'Oh, I'm kind of in pain right now. Oh, I'm having tremors.' If I didn't have this, I probably would be like, 'I don't really care. I don't know what you're talking about,'" she explained.