Jamie-Lynn Sigler reveals her son's terrifying health battle

Jamie-Lynn Sigler has opened up about the darkest moments of her son Beau’s terrifying health battle.

Conversing with PEOPLE, the 43-year-old actress revealed that her 11-year-old son was hospitalised for 33 days due to a rare autoimmune condition.

Sigler, who has lived with pain since she was diagnosed with multiple sclerosis at 20, said, "Those were the hardest days I've ever had in my entire life. It was probably the most helpless I've ever been."

Their crisis started last July after the Love Wrecked star’s "healthy, active" son had a week of high fevers and headaches and then he could not urinate.

"He was screaming in pain," the mother of two shared.

Beau was taken to Dell Children's Medical Centre in Austin, Texas, where he was diagnosed with a rare autoimmune condition called acute disseminated encephalomyelitis, or ADEM.

It causes swelling in the central nervous system and can happen after a viral or bacterial infection.

Singler stated that for the next two weeks in the hospital, "he got worse every day," as “he lost his ability to walk and then to talk. Then he couldn't eat or move his mouth."

"There was nothing recognisable about my son” because he lost 25 pounds.

Doctors gave Beau a 24-hour IV of epinephrine to keep him alive, as swelling in his spine and brain made it hard for his body to control his blood pressure and heart rate.

"My husband and I would look at each other like, 'Is this really happening?' Truly, we thought he was going to die,” The Sopranos actress mentioned, referring to her husband, Cutter Dykstra.

Sigler stayed in the hospital with Beau for more than a month while Dykstra took care of their younger son, Jack, 7.

The Justice alum used what she learned from living with MS to help during that time, quipping, “It was wild to watch my son have neurological issues that mirrored mine in very many ways.”

She continued, "My experience understanding the body and inflammation and the brain helped. From 6 a.m. till 8 p.m., I was on it. I was a coach. I would speak to him and tell him he could do it."

However, "the nights were when I could fall apart and just be a mom and be completely heartbroken and terrified,” Singler admitted.