Sandra, a 45-year-old nurse, has Addison's Disease, a rare disorder of the adrenal glands that regulate hormones essential for life.
If she goes into "Addisonian Crisis" she must be injected with the steroid cortisone and rushed to hospital for emergency treatment.
Mrs Feeney has had two serious episodes so far when her husband Steve, 42, a chemical engineer, had to inject her and dial 999.
But little Harry knows he might one day be called on to help his mother and the youngster is well prepared to spring into action.
Harry said: "I would dial 999 and say, 'We need a paramedic, my mum is unwell'."
Mrs Feeney, from Scotstoun, Glasgow, said: "We had to have a chat about it. I didn't want to frighten him though. I have become quite good at recognising when I am getting ill. I carry a small kit with me all the time. I hope I would be able to inject myself.
"But Harry knows where the keys are to let the paramedics in."
The mother and son are used to looking out for each other. They both have the same kidney condition, Chronic Pyelonephritis, a narrowing of the ureter, which takes urine from the kidneys to the bladder. It means urine can't leave the body as normal, which can cause kidney infections.
But their experiences could not be more different thanks to major medical advances.
As a child, Sandra was in and out of hospital and at one point was a patient for a year. Her condition was diagnosed when the family's window cleaner saw her having a seizure and alerted Sandra's mum.
Prolonged kidney infections throughout Sandra's childhood caused scarring and damage to her left kidney, so it was removed when she was 28, in what was, at that time, major surgery.
Mrs Feeney, who also runs a cake making business, still has problems with her right kidney, including kidney stones and infections and has to have regular check-ups.
She also developed Addison's Disease during the surgery to remove her kidney when her adrenal glands, which sit at the top of the kidneys, were damaged. The condition leaves her feeling very tired and she will require daily treatment for the rest of her life.
In contrast, Harry has just been discharged from regular checks at Yorkhill Hospital For Sick Children because he has suffered no infections for an year and is fighting fit.
Mrs Feeney said: "It was when I was pregnant and going for a scan that he was diagnosed. They could see Harry's kidney was dilated. I was sad and worried because I knew what he would go through.
"I felt so guilty. But they were able to treat him with antibiotics as soon as he was born.
"When he was one, doctors performed an operation to widen his ureter with a stent. He was in for only about an hour. They have now removed the stent and everything is fine.
"The operation was not available when I was little. If it had, I would not have Addison's disease ."
However, she is extremely grateful that advances in medical science have meant Harry has been spared the lifelong treatment she will require. To show her gratitude, she is taking part in the Bridges Walk, a charity event organised by Kidney Research UK, The seven-mile walk is on September 21.
Mrs Feeney has also given her backing to the Evening Times' Opt For Life campaign, which is urging the Scottish Government to introduce an opt-out transplant system, to increase the numbers of organs available for transplant..
She said: "If there is ever any chance I would need a transplant, I would like to think there would be a kidney available, so I should be prepared to donate."
To register for the Bridges Walk see: www.kidneyresearchuk.org/get- involved/events/glasgow-bridges-walk