The Cruel Intentions and Anger Management star posted a glum selfie on Friday alongside an admission about her poor health that day.
"Here's a truth. I feel sick as all hell. I am vomiting and all the things which are not polite to speak of," she wrote. "My son ran away. From me. I have to get him to school. The medical treatments take their toll. I am going to get through this. We do. This will pass."
She also passed on some sympathetic words for parents who may be dealing with children with illnesses.
"And to moms and dads who watch their kids sick on things we want them to take to get better... I hold you," she wrote. "So glad this is me and not my child. I cannot imagine ever feeling ok again. #roughday. But it's still morning. We get through. #realitycheck"
The 46-year-old star later followed up that post with a fully dressed one posted outside. Apparently she convinced herself to get moving, and end up running into fellow actress Sharon Stone, who apparently comforted her.
"I cleaned up. I went out. I got sick. I ran into Sharon Stone and felt comforted," Blair wrote. "She is wise and beautiful. Thank you. #showup and things happen."
Blair, who appears in the new film After, posted a followup photo on Saturday showing herself in better spirits.
"Thank you. For caring. And I send all love. See? Things pass. Or you get sick in prettier clothes. Win win," Blair wrote. "I have the dearest team here. Thank you. Feeling much more life like today. Loving every second."
Blair first revealed her condition in a lengthy message posted in October thanking Netflix executives for the patience they have had while shooting her new show, Another Life.
"I have [multiple sclerosis]. I am in an exacerbation," she wrote. "By the grace of the lord, and will power and the understanding producers at Netflix, I have a job. A wonderful job. I am disabled. I fall sometimes. I drop things. My memory is foggy. And my left side is asking for directions from a broken GPS. But we are doing it. And I laugh and I don't know exactly what I will do precisely but I will do my best."