What would be the worst thing you could develop an allergy to? Pets? Common foods? Pollen? All would demand some lifestyle change but there can't be many allergies more disruptive than a severe aversion to light.
In her memoir, Girl in the Dark, Anna Lyndsey paints a detailed picture of her day-by-day existence with an extremely rare and debilitating case of photosensitive seborrheic dermatitis, where contact with light "burns like the worst kind of sunburn. Burns like someone is holding a flame-thrower to my head."
In what Lyndsey describes as her "life before" she worked for the Department for Work and Pensions until the spring of 2005 when her skin started to react to the glare from computer screens and fluorescent lights, making any kind of office job impossible (as well as bus and train journeys, visits to supermarkets and doctors' surgeries).
She moved out of London to Hampshire, sought help from doctors, dermatologists and photobiologists and tried every scientific and pseudo-scientific method. Nothing helped. By June her condition worsened to include sunlight and at its nadir even exposure to minimum wattage bulbs proved too much.
A prisoner of her own skin, the only thing she could do was to black out her bedroom completely and retreat into the darkness.
Everyday pleasures such as reading a book, preparing a meal or leaving the house became impossible. To keep mentally active she devours audio books, finding a particular taste for SAS survival thrillers. She passes the time with the "trivial earnestness" of Radio 4 and she has phone conversations with people from around the world who suffer with similar conditions, and invents memory-based word games. It is surprising, and distressing, to learn that music is a no-go. When heard in solitary darkness, she says, it "becomes devastating in its power … only a few bars are necessary to dissolve my careful stoicism into wild tears".
Keeping fit is vital since she cannot risk a visit to the doctor, so she does pilates and takes good care of her teeth. And she must never get pregnant.
Lyndsey glides from one topic or time period to another – recalling a dream one minute, describing suicidal thoughts the next – which gives the book a trancelike rhythm (she does provide a chronological timeline in the final pages for those seeking a linear structure).
But this is not just a survival tale, it's also something of a love story. Lyndsey lives with her long-term partner, Pete. Their touching relationship provides some much-needed hope.
There are also periods of gradual remission where she becomes able to venture outside at twilight, providing she wears protective layers and big hats. To be able to step outside after months trapped indoors feels "as though I am being kissed by the world, welcomed back to life". However, if she stays out too long she risks a violent relapse and has to return to darkness for weeks until her skin recovers.
Lyndsey understands that the foremost question an empathetic reader would ask when learning about such a condition is: "How do you cope?" What one really wonders, of course, is "would I cope?"