Christina Applegate is opening up about how "sad" she feels now that her 13-year-old daughter is facing her own medical condition.

The Dead to Me star was joined by her daughter Sadie on Tuesday's (June 25) episode of her MeSsy podcast where they spoke about the teen's recent diagnosis of postural orthostatic tachycardia syndrome (POTS) and how she is bonding with her mom as she continues to face her own health struggles since being diagnosed with multiple sclerosis in 2021, per Page Six.

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

POTS, a condition that affects blood circulation and the autonomic nervous system, causes individuals to experience a rapid increase in heart rate while standing up after sitting or lying down, and includes symptoms like dizziness, fatigue, fainting, exhaustion and more, according to the Cleveland Clinic.

Sadie opened up on the podcast about how she had been experiencing symptoms for a while but they were often dismissed, even as she was visiting the school nurse "multiple times a day" because she "always felt like I was going to pass out."

"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,'" she recalled, adding, "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."

The teen said the school's dismissal "hurt me physically and emotionally." Even Applegate admitted to not taking the symptoms seriously as she didn't understand the condition, something she feels "horrible" about now.

"I just didn't see it at home, babe. At home you were find. But it's kind of like us," Applegate told her daughter. "We get out in the world, and the stresses and the anxiety of the world bring upon our symptoms much worse than they would be if we were in the safety and the coolness of our own homes."

She added, "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."

Billy & Lisa in the Morning