One night I woke with a jolt, gasping for breath. My tongue was so swollen it was filling my mouth, and something was pressing on my throat. Panic pulsed through me as I realised I couldn’t breathe through my blocked nose either.

It wasn’t until I heaved myself upright that I was able to take small gasps of air. Careful not to wake up my husband and two young children, I made my way downstairs to dial the out-of-hours NHS emergency helpline.

Only when a dose of Ibuprofen eased my symptoms did they agree I could wait to see a doctor in the morning, rather than rush to A&E.

Why was I reduced to this pitiful state? I’d developed a life-threatening secondary infection to a viral disease that I am not alone in thinking was wiped out decades ago: mumps.

This was a common childhood illness until the introduction of the MMR vaccine in 1988. Symptoms include painful swellings at the side of the face and a high fever.

Emily Cleary, 40, (pictured) was told she stood the chance of developing life-threatening meningitis after contracting mumps as an adult

But the indignity of resembling a hamster is nothing compared to the other risks when you contract mumps as an adult.

I was told that due to my age — 40 — I stood a chance of developing life-threatening meningitis. I was also at risk of glandular fever, tonsillitis, pancreatitis and other secondary infections. And if your glands and throat swell to the extent mine did, you could even choke to death.

Frightening stuff. So why had I succumbed to such a dangerous, but easily preventable disease? After all, my children, aged five and three, had been vaccinated for free by the NHS.

The reason is what I believe is the wilful ignorance of parents who form part of the growing movement of ‘anti-vaxxers’.

Inspired by ideas about ‘clean’ living and that putting any sort of chemical into our bodies is harmful — even ones designed by doctors to help us — they prevent their children from having MMR and other childhood jabs.

They ignore the absence of any scientific evidence while pooh-poohing the risks of their children catching mumps, let alone passing it on to adults who lack immunity. My doctor told me she had only seen one other case of mumps in the past 15 years. So how did I come to have it?

Well, born in 1978, I grew up before the MMR vaccine programme was introduced and after checking with my mother, I discovered I had not caught mumps when everyone else did at primary school.

My GP asked if I had been abroad recently — some countries don’t vaccinate to the same schedule — but I hadn’t. I had, however, spent most of the summer in and out of soft play centres with my children, and visited a holiday park on the south coast of England.

So, she concluded I must have caught it from an unvaccinated child, who may have contracted it on holiday abroad. All they would have needed to do was cough in my direction, since mumps is spread by airborne droplets like the common cold.

Emily (pictured before) believes she unknowingly put the lives of a newborn baby and seriously-ill cancer patient at risk by coming into contact with them in the weeks leading up to her illness

From that moment, I was a risk to anyone who hadn’t been vaccinated or had mumps before — especially anyone with a weak immune system.

I was horrified to recall that in the two weeks leading up to my illness I’d come into contact with a newborn baby and a seriously-ill cancer patient. By unknowingly carrying this virus, I had put their fragile lives in danger. Which means that by choosing not to immunise their child against mumps, a parent had also put these lives at risk. My anger knew no bounds. How could anyone be so thoughtless?

And yet the militant anti-vaxxer movement seems to be gaining momentum with supporters such as Donald Trump — who has tweeted more than 20 times suggesting a link between vaccines and autism (which has never been proved). Last year more than 40,000 people signed a Change.org petition against any type of vaccines becoming mandatory in the UK.

Having been raised by a mother with a degree in molecular science and a career in the pharmaceutical industry, I’m in no doubt about the importance of vaccination programmes. But I have met mothers who vehemently disagree. One anti-vaccine friend told me, ‘All I care about is my child, I don’t care what effect not vaccinating may or may not have on others.’

I was shocked and angry. I bit my tongue. Another told me she lied to her daughter’s school when they asked if she’d had her jabs. ‘It’s none of their business,’ she said, adding that she suspected vaccination programmes were a money-making ploy by the Government and drugs companies.

Emily's husband was told that he could've been left infertile if he contracted mumps from being in contact with her (file image)

British anti-vaccine network Arnica encourages parents to meet to ‘discuss vaccine issues’. It believes most illnesses can be treated homoeopathically, or avoided altogether with the correct diet. The group’s website claims: ‘When we compare a vaccine’s possible adverse reactions, and possible longer-term health problems, against complications from childhood disease in healthy children … in most cases the non-vaccinated child is healthier.’ They fail to back this up with science or facts.

Members suggest a daily dose of Vitamin A could protect against measles, and that the MMR vaccine causes bowel infections, Crohn’s disease, even epilepsy. Medical professionals have rubbished these claims.

So, if a parent doesn’t vaccinate, their child may catch mumps — and pass it to me and who knows how many others. I then may infect dozens more innocent people before I am even aware I have it.

If growing numbers of children aren’t vaccinated, this scenario could become commonplace astonishing quickly.

When should babies have their first jabs? The MMR vaccine protects against mumps, measles and rubella. The first injection is given within a month of a baby’s first birthday Advertisement

Meanwhile, my face sore and fatter than a squirrel collecting nuts for winter, I was playing the waiting game. I felt, and looked, worse every day. My head was constantly pounding, my appetite non-existent.

For three days I wasn’t able to cook, play with my children, or even bath them and put them to bed. At first they laughed at ‘Mummy’s funny face’, but after a couple of days it began to unsettle them. They couldn’t understand what was happening.

As a PR consultant, I missed meetings. More importantly, I also missed my son’s first week at school. Barred from going to pick them up in case I infected others, my husband had to take time off work to do the school run.

On the fourth day of my illness, my GP deemed me an official ‘public health risk’. He was shocked at the severity of the swelling and diagnosed a secondary infection — streptococcus. I was prescribed strong antibiotics and told to stay in bed for a further three days.

I was also warned not to lie flat because I might choke to death, and to regularly monitor my temperature and swelling because I was ‘on alert’ for A&E.

Two months later, I am on my third intensive course of antibiotics as the secondary infection keeps recurring. I have also been diagnosed with post-viral fatigue, which has left me bed-bound and suffering debilitating migraines.

I have been warned these effects may last for months, even years.

Following my diagnosis of mumps, my husband and I faced a three-week wait to see if had contracted the virus, too. If he had, it could have left him infertile. Thankfully, he hadn’t.

All this because I must have been in contact with a child whose parents didn’t bother to immunise them. I am starting to recover — but others might not be so lucky.