Blood tests showed that the 24-year-old Tyrone captain died of a condition affecting about one in 100,000 people.
As his body was taken to his family home in Eglish, Co Tyrone, seven miles from Dungannon, his grieving mother, Bridget, described how they fought desperately to save his life.
Mrs McAnallen, speaking for the first time about the tragedy that has rocked her family, said she attempted artificial respiration on her stricken son. "When I went into Cormac's bedroom, I knew there was something wrong. I looked for signs of life. I started to feel for a pulse but I couldn't feel it straight away."
She revealed that an ambulance crew which arrived at the house worked for an hour to resuscitate her son, but nothing could be done.
Mrs McAnallen had been alerted by Cormac's distraught older brother, Donal, early on Tuesday morning. As the family waited agonisingly for the ambulance to arrive, she rang a family friend, Dr Anjun Ghosh, for help.
"I asked him how to do artificial respiration. We had already started to do it at that stage, but none of us could be sure we were doing it perfectly," she said.
Both Dr Ghosh and the ambulance crew attempted to resuscitate Mr McAnallen but without success.
A crowd of around 300 people, including members of Mr McAnallen's home club, St Patrick's, stood silently in Eglish as his hearse, followed by more than 50 cars, wound its way through the village towards the family home.
The club's former chairman, Canice Murtagh, said the people of the area were devastated by his death.
"Football has gone out of the window. He was more than a hero. I don't think anybody could describe what Cormac McAnallen meant to this community," he said.
The family have been touched by the messages of sympathy by people from all walks of life.
They included President Mary McAleese, who phoned the family yesterday. "She was just full of help, sympathy and understanding. She praised Cormac's achievements," said Mrs McAnallen, who said she was struck by how much her son's death had affected everyone in the community.
"I'm quite amazed. I knew Cormac had a very high profile before that and did seem to be universally loved among GAA people, but I didn't realise how far and wide his reputation has spread."
Despite his successes on the field, which included last year's victory in the Sam Maguire Cup, she said Cormac had remained the same modest young man he had ever been.
His brother Donal, 25, spoke graphically about the last moments of his brother's life. He heard what sounded like loud snoring from his brother's bedroom. "It got so loud so quickly I thought it might be a prank."
He ran up the stairs and found Cormac lying on his side staring straight ahead.
"He gave a last wheeze and I told him to snap out of it, but he didn't. I just heard the very last gasp from him. It was shocking, it will be a horrendous memory for me. We were very close."