Christina Applegate's daughter Sadie LeNoble is navigating her own health struggles.

Amid the Dead to Me actress' journey with multiple sclerosis (MS), her 13-year-old daughter has been diagnosed with Postural Orthostatic Tachycardia Syndrome, also known as POTS, which can cause symptoms such as fast heart rate, dizziness and fatigue when transitioning from sitting or lying down to standing up. 

"When I stand up, I get really, really dizzy and like my legs get really weak and I feel like I'm going to pass out," Sadie explained on the June 25 episode of her mom's MeSsy podcast." And I have fainted before and I have gone unconscious, but that doesn't usually happen."

And while the diagnosis has presented certain challenges for the teen—especially while at school—it has also helped her better understand her mom's struggles. 

"I feel like if I didn't have this thing, it would be a lot harder to understand what my mom's going through," Sadie, whose dad is Christina's ex-husband Martyn LeNoble, shared. "When my mom's like, 'Oh, I'm in pain right now. Oh, I'm having tremors.' If I didn't have this, I probably would be like, 'I don't know what you're talking about.' But I have tremors from POTS."

She added, "It's definitely a lot easier to understand what she's going through when I have something I'm going through as well."

Since the 52-year-old was diagnosed with MS in 2021, their lives have drastically changed.

"Every night, I remember when I was a kid, we would dance and everything in her room for like hours at a time," Sadie said. "When she got diagnosed it kind of just felt like—not like everything was over, but it was hard seeing my mom lose a lot of the abilities she used to have in my childhood."

And for Christina, her inability to do some tasks she used to do for Sadie has been difficult. 

"When I do say I'm having a bad day," she said to Sadie, "I always feel incredibly guilty about having to say that because I don't ever want you to feel that I'm not capable to be your protector, your mother. I love you. I want to make you food. I want to bring it to you. I want to do all the things. And I do when I can. And I feel incredibly guilty when I can't."

Though the Married With Children star added, "But you're always pretty darn cool about it, kid."

Keep reading for a look at Christina's health journey.

Christina Applegate shared she was diagnosed with multiple sclerosis in 2021.

"Hi friends. A few months ago I was diagnosed with MS," she shared on her social media channels that August. "It's been a strange journey. But I have been so supported by people that I know who also have this condition. It's been a tough road. But as we all know, the road keeps going. Unless some a--hole blocks it."

"Oh, by the way, I have a disease," she joked during her November 2022 Hollywood Walk of Fame induction ceremony, her first public appearance since her MS diagnosis. "Did you not notice? I'm not even wearing shoes."

Christina believes her MS journey actually began "six or seven years" before her 2021 diagnosis.

"I noticed, especially the first season [of Dead to Me], we'd be shooting and my leg would buckle," Christina explained during a March 2024 interview on Good Morning America. "I really just put it off as being tired, or I'm dehydrated, or it's the weather. Then nothing would happen for months, and I didn't pay attention."

By the time she was shooting the Netflix series' third and final season, the actress said she was "being brought to set in a wheelchair."

"I couldn't move that far," she recalled, "so I had to tell everybody because I needed help."

The Dead to Me star captioned this photo of her cane collection amid her battle with MS: "Walking sticks are now part of my new normal."

Joined by her daughter Sadie Grace LeNoble, Christina had a simple message for multiple sclerosis while attending the 2023 SAG Awards: "F U MS."

After a receiving standing ovation at the 2023 Emmys, the Married...With Children alum quipped, "You're totally shaming me with disability by standing up."

"I make these jokes because if I don't, I'll suffocate," Christina shared on a March 2024 episode on Armchair Expert, explaining why she often pokes fun at her condition. "I'll be done."

"I have 30 lesions on my brain," she said on the same podcast. "My biggest one is behind my right eye, so my right eye hurts a lot."

Legions are caused by the immune system attacking the myelin sheath around nerves, according to the Multiple Sclerosis Trust.

Christina hasn’t held back when it comes to sharing her journey. 

"It sucks," the Anchorman actress told late night talk show host Jimmy Kimmel of her daily struggles with MS. "I'm not going to lie. I think anyone who has MS isn't going to be like, 'This is the best thing that ever happened to me!'"

When talking about her day-to-day life with the disease, Christina told Good Morning America in March 2024, "I live kind of in hell."

"But I might get to a place where I function a little bit better," she added. "Right now, I'm isolating, and that's kind of how I'm dealing with it—by not going anywhere because I don't want to do it. It's hard." 

Christina credited her Sweetest Thing costar Selma Blair—who was diagnosed with MS in 2018—for urging her to get tested for the disease.

"She said, 'You need to get checked for MS,'" Christina recalled during her GMA interview. "If not for her, it could've been way worse."

Christina confirmed that Dead to Me will likely be her last onscreen credit, telling Vanity Fair in May 2023, "I can’t even imagine going to set right now."

"I’m probably not going to work on-camera again, but I'm so glad that I went out with someone who is by far the greatest actress I’ve ever worked with in my entire life," she said of costar Linda Cardellini, "if not the greatest human I’ve ever known.