My hair was long and fair before it all fell out suddenly, along with my eyebrows and eyelashes, when I was just 20. In five days, it was reduced to just a few small patches. I felt I’d lost a lot of my femininity. You don’t realise how much hair changes the look of your face and your sense of identity. It happened because of a rare condition – mast cell activation syndrome (MCAS) that meant that my body had rejected my hair follicles. The first signs of this syndrome started five years ago, when I was 18. I was out with friends at an event at Liverpool Docks and started to feel really unwell. I went to see a first aider, and the next thing I knew, I was being resuscitated in hospital. They said I’d had an anaphylactic reaction, and that it was probably a one-off. Then the same thing happened two days later. I couldn’t believe it.

It took more than two years to get diagnosed. I’ve probably had around at least 500 life-threatening allergic reactions since then. MCAS was first recognised as a condition in 2007. It means that white blood cells in my body are faulty. The allergiv reactions happen spontaneously, at least once a day. I might be watching TV or even be asleep. I’m potentially allergic to everything: alcohol, crying, or changes in the weather. With my hair, my cells were fighting the follicles, which made it fall out.

I get treated as an allergy patient, but there’s not a lot known about the condition. People debate whether it exists at all. I’ve been made to feel by some people, even doctors, that it’s all in my head. Some days I’m more sensitive than others. I could eat something today that won’t provoke a reaction and eat the same thing tomorrow and nearly die. It all depends on the cells. They are like moody teenagers.

It’s difficult, because you never know when it’s going to happen. The first sign is that my tongue goes numb and starts to swell. Sometimes I can focus on my breathing and take medication, such as injecting myself with EpiPens, and hope that it calms down. But often it gets a lot worse and I may even stop breathing. I feel as if I’m burning. Some of the attacks last for 10-20 minutes, but others go on for days or weeks, and I end up in intensive care.

When my hair fell out, I had to make more of an effort with my makeup, otherwise people would address me as “sir”. Odd patches of hair would grow through, but when they did, the skin would blister and I’d have to shave it off, or it would send me into anaphylactic shock. Now, happily, the cells that were responsible for my hair falling out seem to have died off, and it’s growing back. It feels good, but also strange: I’ve even had to go out and buy shampoo (I hadn’t needed to wash my hair for two years). I think my hair will now keep growing until the cells change their mind again.

My parents are amazing. They moved more than 100 miles so I could be near a better doctor, and to a bungalow so I didn’t have to manage stairs when I have problems breathing. I don’t have any siblings, so we don’t know if it’s hereditary.

It’s hard to meet people. I can’t exactly put on my Tinder profile, “I might die and need you to stab me with a needle if I get sick.” My friends are getting engaged and travelling and graduating, and I’m sat here. I’ve always loved gymnastics, and have been doing it since I was eight. Now, I’m an elite disability gymnast and have 22 British titles and 36 medals. I love it, but if someone said I could trade all my medals for a cure, I’d take it.

Doctors have no predictions for my future. I might wake up one day cured, but I think we’ve passed that point, because I’ve lived with it for so long now. So, instead, I’m focusing on quality of life, rather than quantity. My heart has been damaged by all the adrenaline, so who knows how long I’ve got?

I try to be strong, but other times I want to shout: “This is not fair. I feel really awful, and no one knows how to help me.” But this is obviously the life I was meant to lead, so I’m going to try to do my best with it.

• As told to Sophie Haydock. Do you have an experience to share? Email experience@theguardian.com