But rather than beating himself up, he decided to change his attitude.
The only option was to leave his support network and travel to Boston where he would spend the next few months receiving the ground-breaking CAR-T cell therapy, available only in the US and more recently Europe.
"It was this really incredible and challenging period, but it was an amazing opportunity ... there was no other option. It was either that or crawl into a corner and die," Downs said.
Through a variety of measures, he managed to raise enough to get started on the process.
"For the next two or three weeks, it was head down bum up, trying to solve all these problems. We didn't have time to think of the alternative, because we knew we had to move fast. It was quite incredible what we were able to achieve."
The therapy works by taking the immune cells - known as the T cells - out and genetically engineering them into "killer cells" before inserting them back into the blood.
Downs believes the experience of having CAR T-cell therapy was "just trivial". "It was like having a blood test - an injection, instead of having months and months of chemotherapy which nearly killed me."
But in a matter of months, he has gone from being on his deathbed to having his whole life ahead of him.
Now, the 47-year-old, along with the Malaghan Institute is trying to get the same treatment which saved his life, to New Zealand.
"Other people shouldn't have to go through what I went through."
"I feel like I owe it to society to do everything I can to bring it to New Zealand so others can have that same chance of survival as I did."
Through his campaign, 'Down with Cancer', he has pledged $1m that he hopes will be raised in less than a year. And has already raised more than $40k in two weeks.
"I'm trying to raise awareness that this is a seriously big opportunity to change the game for cancer research and treatment in New Zealand."
As part of the campaign, he spoke at Lexus Hawke's Bay in Hastings on Wednesday evening.
For more information visit: https://www.malaghan.org.nz/down-with-cancer