A woman delivering prescriptions found a man, 84, struggling to breathe at his home but had not called for help thinking "everybody was too busy".
Amanda Hellman, 50, was outside his house in Cambridgeshire, when he knocked on his window to alert her.
She entered the Littleport home and found him "quite distressed". He was later taken to hospital.
Ms Hellman said: "I don't like to think of the consequences if he'd stayed there on his own."
The man, who has not been named, is expected to be released from hospital later.
Ms Hellman, who with partner Dean Abbass runs a motorcycle training school, said they were "utilising our skills to help people in this quite dreadful situation" during the coronavirus outbreak.
On being alerted by the man, Ms Hellman went round to his back door, which was unlocked, and found him "really quite distressed and struggling to breathe".
He told her he had needed oxygen for two days, but it had not been delivered. She asked him why he had not called for help and "he just said, 'everybody's too busy at the moment'."
Ms Hellman then rang for help and paramedics arrived to take him to hospital.
She said: "Everybody keeps going 'you've potentially saved his life' but to me I was just doing what any normal person would do.
"Somebody needed help, I made sure he got it and sat with him."
Ms Hellman, who is out delivering for between 10 and 12 hours a day, says it highlights the need for people to check in on those self-isolating.
"[They] may actually genuinely believe that everybody is too busy to help them and they're not asking for help," she said.