A few weeks ago I was at home when, out of nowhere, I began to feel dizzy. Within minutes, I was throwing up, then horizontal on the bathroom floor, unable to speak or get up.
I thought: 'Oh, no, not again.' This was the third time this had happened.
The first time, about six years ago, my then 20-year-old son rang 999. He knew I was ill because I wasn't someone who was usually sick. In fact, I hadn't vomited in nearly 50 years. I went to A&E and was put on a drip but recovered after a few hours and was sent home without a diagnosis.
On this most recent occasion, I had driven back from France with my boyfriend the day before. I hadn't managed to eat much on the move.
The following day, one minute I was fine, the next I was lying on the carpet and feeling like death.
My son rang my boyfriend, who raced back from work, but they didn't call 999. After five hours, I felt relatively normal again, if weak. I now know it isn't life-threatening, even if it might feel like it.
After my previous collapse, a neurologist diagnosed me with a condition called Postural Tachycardia Syndrome (POTS). It makes your heart rate increase rapidly after getting up from sitting or lying down, making you dizzy and lightheaded. It also causes fatigue and brain fog and affects 0.2 per cent of the UK population, although its prevalence is increasing.
Mainly affecting women, it tends to strike between the ages of 13 and 50 (although I was in my mid-50s when I was diagnosed; I am 61 now).
The public became more aware of POTS in 2015 when Ella Mills, of the Deliciously Ella brand, published her cookery book. She was a sufferer but, at first, doctors were dismissive or baffled by her debilitating symptoms. She became desperate and eventually devised a healthier diet to help reduce them.
Many people with POTS also have Ehlers-Danlos syndromes (EDS) - although I don't. POTS and EDS affect the connective tissue (the glue) which holds everything in the body together and can make the joints, skin, organs and blood vessels much weaker and stretchier.
In 2018, Jane Green, who suffers from EDS, started SEDSConnective, a charity which supports people with these conditions.
She says doctors usually look for POTS over a few months. In adults, they see if your heart rate increases by more than 30 beats per minute within ten minutes of standing, without blood pressure dropping. They may also do heart tests such as an ECG to rule out other causes.
In my case, hot weather often sets it off - my hands and feet swell up and I can feel heavy and sick. After my diagnosis, doctors said I had to drink more water and eat 12g of salt a day.
I mostly work from home writing novels, so I have been able to manage my POTS with water and foods such as bananas and dates to stave off a dizzy spell.
But a recent project has made managing my condition more difficult. I'm launching a publishing venture called The Authors' Collective. This has involved lots of meetings and being less solitary and sedentary than normal - leaving me more vulnerable.
On my way to a meeting in London recently, I felt sweaty and nauseous on the train.
Before going into the office, I had to sit for a few minutes, take an electrolyte, breathe deeply and cool down.
The neurologist recommended I consume two electrolyte drinks a day, so now I never leave the house without sachets in my bag.
Eating healthily and exercising regularly - but carefully - helps, too.
If there is any consolation to having POTS - and I don't mean to sound flippant - then it is that I'm less wrinkled than I might have been.
Jane Green looks more than 20 years younger than her age and says it's down to the stretchiness of her collagen.
I still needed make-up at the launch of The Authors' Collective though. Most people, if making a speech in front of hundreds as I did, might quaff a beta blocker to calm their nerves. In my case, to avoid falling off the stage, I glugged an unglamorous Dioralyte instead.