Blackwell was forced to quit boxing after a bruising British middleweight title defeat to Eubank Jr left him in a coma for a week in 2016.
The 26-year-old from Trowbridge, Wilts., collapsed in the ring minutes after the fight with a bleed on the brain that ultimately led to his retirement from the sport.
But in November that year, Blackwell was taken to hospital after being taken ill following a sparring session and needed an operation to reduce the swelling on his brain.
“The hairs stand up when I think how far I have come,” Blackwell told The Telegraph.
“I died in the ambulance after the Eubank fight. They brought me back to life.
“The second time, they cut a section out of my skull to relieve the swelling on my brain. They placed it inside my stomach to keep it alive until it went back. Crazy.
“I was told there was a 75% chance of dying.
“If I survived, there was an 85% chance of being paralysed down my left side. And guess what? I am going to run a half-marathon next month.
“I want to raise money for the people who saved me.”
Blackwell explained that his “addiction” to boxing is what prompted him to get back into the ring that November to spar with Hasan Karkardi, who was getting ready for a Southern Area light-heavyweight title fight.
Karkardi said he didn’t know who Blackwell was.
Blackwell said: “I love boxing. It was my life. An addiction. I felt really good again. He came to the gym and it was, ‘Who wants to spar with him?’ I said, ‘I will’. It used to be that I wouldn’t say ’no’ to anyone. I missed it so much that I didn’t really consider the risks.
“I was told there was a 75% chance of dying”
“You think that you’re invincible. It’s my own fault. No-one else to blame.”
Blackwell was in a coma for a month and needed to use a wheelchair. He is now preparing to run the Weston-Super-Mare half marathon.
Eubank Jr – son of eccentric former World Champion Chris Eubank – meanwhile, fights James DeGale tonight at the O2 Arena in an IBO super middleweight world title fight.
Daily Star Online previously revealed the Brighton brawler showing off his mansion to fans ahead of the bout.