"One minute I was sitting there and, the next, I woke up on the floor surrounded in blood. I was totally mystified as to what had happened."
She called her husband who came home and initially thought an intruder had been inside and had hurt his wife.
"I had a gash on my head from the fall that had resulted in the blood."
Taken to hospital by ambulance, tests were done including a CAT scan, but it was determined McGrath had concussion from her fall and she was sent home.
Then it happened again a few days later. The second time she "wrecked" her other eye in the fall.
After an overnight hospital stay and an appointment with a neurologist, McGrath was taken home by her mother who had arrived from Auckland to help.
"When we got home I blacked out again. But this time mum was there and she was able to tell me I had started coughing and continued coughing until I blacked out.
"By this stage my GP had become aware of what was happening and called me in. I told her what had happened and she immediately sent me off to be tested for whooping cough. The results were positive and I was put on antibiotics."
McGrath said, at that stage, it had been 12 years since she had been vaccinated for whooping cough.
If she had become pregnant in that time she would have been administered the vaccine to protect herself and the baby, but that had not happened.
In spite of the antibiotics the coughing and passing out continued for months.
"It was awful. I was paranoid I was going to give it to someone else, I felt like a prisoner in my own home."
She said her husband used to lie awake at night listening to her cough and wonder if she would come out the other side alive.
As well as seeing a respiratory specialist, and having surgery to remove gunk from her lungs, McGrath took a year's unpaid leave from her job to focus on getting better.
"I'm so lucky I had a supportive husband, family and employer – I can't even imagine trying to get through what I did if I had other responsibilities."
McGrath said she is just starting to feel okay now.
"Whooping cough epidemics are cyclic [they happen every three to five years] and we are in a cycle now. Please everybody, make sure you are vaccinated so you don't have to go through what I did."
Toi Te Ora Medical Officer of Health Phil Shoemack described whooping cough as a terrible illness.
He said there hadn't been any deaths due to the disease in the past five years but there had been in the past decade.
"The striking thing about people who contract whooping cough is that they are often very young babies," Dr Shoemack said.
"Babies are very susceptible early in life because of their size and the capacity of their lungs."
He said although immunisations were given at 6 weeks, 3 months and 5 months, it wasn't until after the last vaccination that a baby had built up an immunity.
"The thing we are seeing now is that adults get a persistent cough but wait three or four weeks before going to see a doctor. By the time they are treated they have already given it to a child or children."
In adults whooping cough is most often less extreme. He advised adults who developed a cough to seek medical attention early in the illness.
A total of 49 cases of whooping cough were recorded by the Lakes District Health Board in 2017 but from December 16, 2017, to January 12, 2018, 11 cases have been reported.
None of the 11 people required a hospital stay and only one was under a year old.
Last year two people were admitted to hospital as a result of whooping cough.
Nationally, 380 cases of whooping cough were notified in the past four weeks, significantly higher than the 120 cases reported in the same period in 2016/2017.
From the beginning of the current national outbreak period (October 16, 2017) until December 31, 2017, a total of 967 cases have been reported throughout the country. Of these 967 cases, 576 have been confirmed, 367 are probable and 24 are suspect. A further 50 cases are still under investigation.
