"My tumour was 16 centimetres across, it was like having a brick in my chest, so no wonder I was throwing up after trying to run," recalls Jersey Reds fly-half Sam Leeming.
Six rounds of chemotherapy followed as Leeming's body fought the cancer of his lymphatic system.
"I thought I was just unfit," Leeming told BBC Radio Jersey as he recalled last year's pre-season for the island side.
He had just moved to the club from Bedford Blues, but as his first fortnight at his new team continued, he knew something was not right.
"One morning my face was really puffy, it was because my tumour was pressing against my pina vena cava (a blood vessel to the heart) and the blood wasn't draining from my head," Leeming explained.
"Coming off a front squat in the gym, in the sessions that I was doing, I was feeling really light-headed."
'The word cancer is such a heavy word'
Leeming says at one point his heart rate was 197 beats per minute just in the warm-up - a level he should have been hitting if he was in the middle of a very tough workout.
It led the Jersey Reds' medical team to do some tests and he was sent to see a doctor - very soon after, he was diagnosed and came back to the UK for treatment.
"So many cancers just get missed because it is invisible to a certain extent," Leeming reflected, having recently been given the all-clear to resume training and begin his career at Jersey Reds for a second time.
"They go unnoticed under the skin for so long, that's why it causes real problems, because people don't pick it up early enough, so I'm incredibly lucky.
"The word cancer is such a heavy word," he added.
"I couldn't say it for the first month at least because it carries so much weight, there's so much unknown to it all, the more you learn about it, the more getting the good news about the type and how treatable it was, just little wins like that make a huge difference."
Due to the Covid-19 pandemic, Leeming had to face his cancer treatment in hospital alone - and undergoing treatment on his own gave him a chance to reflect.
"It made me realise what a lucky position I'm in," he added.
"Anything we want to do now, whether it be my girlfriend or my parents, we just go and do it because at the end of the day I could have been gone before Christmas. You can't stall through life.
"I smile about it now because there were some absolutely grim days in that hospital, the stuff you hear from next door rooms or the people you see who were in so much worse condition than I was.
"I felt incredibly lucky and it gave me the strength to keep cracking on."