He ran away from the hospital that day, fleeing the consultant's words about bladder cancer and what it might mean.
Instead he set about planning his own funeral, passing on his treasured possessions to the two adult children he thought he would soon be leaving behind.
Had he paused to ask for guidance, he admits today, he would have saved himself the torture of what was to follow.
"I didn't realise that not asking for help destroys you inside," says the 55-year-old from Rotherham.
"It's not a weakness, to need support. I didn't ask for help, it was forced on me. It was the best thing that could have happened.
"We all need to learn to be better at asking for help."
Mr Casey, an Army chef of 12 years posted to Germany, the Falklands and Cyprus, is a standard bearer with the Royal British Legion in Dinnington and district.
In August last year, he travelled to Belgium and France with the branch to honour a pilgrimage of remembrance to some of the First World War's most poignant sites.
While away, he began to feel unwell, and noticed there was blood in his urine. Tests were to reveal it was bladder cancer.
"I got myself into a severe panic," said Mr Casey. "The consultant was talking but I couldn't listen, take in the words. I just wanted to get out of there.
"I could feel myself welling up, and the nurse said it would be OK if I cried. I refused, I just ran out of that hospital.
"I came away thinking I had prostate cancer, then bowel cancer. I didn't have a clue. I live on my own and, without anyone to stop me, I withdrew into my own world."
In the days that followed, Mr Casey says, he went to a "dark place". He didn't leave the house, stopped washing or shaving.
It was a colleague from the Royal British Legion, he said, that intervened. They put him in touch with Macmillan - a charity he had until now always associated with women.
Between the two groups, there was financial assistance, shopping support, a nurse who attended consultant meetings with him and explain in layman terms what to expect.
It made a huge difference, says Mr Casey. Even something as simple as a toilet pass that Macmillan organised, which means he can access bathrooms while he is out of the house.
“It was only when I spoke to my Macmillan nurse did I fully understand that I had bladder cancer, I’d never even heard of bladder cancer before," said Mr Casey.
“The nurse was able to break it down for me in really simple terms, that’s what I needed.
"I wouldn't be here without them," he adds. "I was in a dark place. I was so lucky, to have such fantastic people around me.
"I'm getting there, slowly. Now I live every day to the best I can. I looked normal, happy. People think disabled is only something you can see."
Mr Casey has had a tumour removed, and is still undergoing treatment for bladder cancer. He is now a committed fundraiser for Macmillan support and for the Royal British Legion.
"I do a lot of charity work," he said. "I can’t do anything about my cancer, what I can do is give something back. It’s for me, fundraising gives me a purpose.
“I think men are their own worst enemies," he adds.
“I’d be dead without Macmillan support. My mental wellbeing was so low, I know I was at the end of the line.
“To know whatever cancer you have there’s a massive support network going on behind the scenes makes a big difference.”
Dinah Coggon, Macmillan partnership quality lead for South Yorkshire she said: “Ali’s story shows that cancer is not always life threatening, but it is life changing.
“Regardless of the diagnosis, life will never be the same again.
“At least one in four of those living with cancer - around 625,000 people in the UK - face poor health or disability after cancer treatment.
“Macmillan funds cancer nurses, information and support workers and other health professionals across Yorkshire to help ensure people with cancer get the physical and emotional support they need.”