Selma Blair experiences 'rough day' amid MS battle

May 3 (UPI) -- Selma Blair is having a "rough day" amid her battle with multiple sclerosis.

The 46-year-old actress shared a message of perseverance Friday while feeling "sick as all hell" from her treatments for the disease.

Blair posted a photo of herself lying down on what appeared to be her son's bed. She is parent to 7-year-old son Arthur Saint with Jason Bleick.

"Here's a truth. I feel sick as all hell. I am vomiting and all the things which are not polite to speak of. My son ran away. From me. I have to get him to school," the star captioned the post.

"The medical treatments take their toll. I am going to get through this. We do. This will pass," she said.

Blair voiced her support for other parents struggling with illness.

"I hold you," she wrote. "So glad this is me and not my child. I cannot imagine ever feeling ok again. #roughday. We get through. #realitycheck," she said.

Blair went public with her MS diagnosis in August. She recalled her emotional reaction to her diagnosis in an interview with Good Morning America in February.

"I cried," the actress said. "I had tears. They weren't tears of panic. They were tears of knowing that I now had to give in to a body that had loss of control and there was some relief in that."

"Ever since my son was born I was in an MS flare-up and didn't know," she shared. "I was ashamed and I was doing the best I could ... so when I got the diagnosis, I cried with some relief."

Blair is known for the films Cruel Intentions, Legally Blonde and Hellboy.