The former Brookside star is among the celebrity contestants on the latest series of the Channel 4 military training and survival show and has detailed how jumping from a helicopter caused bleeding from her lungs and spleen.
Ellison, 39, told The Daily Star: "After I jumped from a helicopter, I hit my ribs and then I could feel a pain in my side.
“When I got back to the UK it was getting worse, so I went to A&E.
“They told me, ‘You’ve got broken ribs, blood in your lung and a bleeding spleen’. The infection in my lung was really nasty.”
The soap star and mother-of-three – who won Gordon Ramsay's cooking reality show Hell's Kitchen in 2004 – admitted it took a "very long time" to recover from the injuries, that left her "laid flat" in bed and struggling to breathe.
Ellison – who has three sons aged 12, nine and seven with boxer husband Rob Tickle – said one of her greatest fears was leaving her family to film the show on location in Jordan.
She said: "I'm afraid of being away from the kids. I'm afraid to sleep away from my husband, so that even in itself was a massive thing for me."
The former soap star and West End performer, who rose to fame playing Emily Shadwick in Brookside, described Celebrity SAS as "inhumane".
She said: “There were times when I worried about dying. I was thinking ‘What they’re doing to us cannot be legal’."
But Ellison – who appeared in Lifetime reality show Dance Moms in 2014 – said that despite experiencing "the worst pain imaginable" on the show "the reward was life-changing" and she would recommend taking on the challenge to other celebrities.
Celebrity SAS: Who Dares Wins airs on Sunday at 9pm on Channel 4.
Watch: Kerry Katona on taking part in Celebrity SAS