In 1987 I was diagnosed with HIV. Back then, it was a death sentence. I watched friends and loved ones dying around me. I’d served in Vietnam and it felt like something similar: one amazing person after another falling away. All still young. All still with so much to live for. Somehow, I survived both, and since the 90s have constantly been on different medication that has kept me alive. But 10 years ago, one of these drugs – or some combination – wrecked my body in a way doctors still don’t understand. Aged 53, over a period of three or four months, I became allergic to light. I have had to live in pitch black ever since.

It was 2007 when I started breaking out in an itchy, burning rash. It would start suddenly on my neck, then spread to my face, chest, shoulders and back. Doctors assumed it was a medical allergy and changed my prescription. But it got worse until at times my whole body felt on fire. It was as if my skin was being held against a flame, searing for days on end.

I used to sing in a choir and I noticed the rash would be most severe in the days after practice. Then, one afternoon, I was outside in the shade with just my feet in the sun. I felt a tingling on my ankles and noticed my neck blistering. I thought about the choir and how we stood under bright lights, and something clicked. I told my doctor and, after tests, I was diagnosed as photosensitive. Exposure to light on any part of my body caused the skin on my neck, face and torso to burn. They told me there was likely no cure.

Leaving home became almost impossible. I kept the curtains drawn, but just the light seeping in at the edges caused irritation. Watching TV became painful. Even opening the fridge would set my body tingling. I was an artist but I couldn’t switch on the lights to work. I didn’t know how I was going to live. But I also knew I wasn’t going to let this beat me.

Carrying on living where I was wasn’t practical: I needed somewhere with fewer windows and closer to hospital. I had an art studio in the bowels of an old building in San Francisco and the owner let me convert storage space there into an apartment, where I’ve been since.

My friends and two grown-up children helped me arrange everything. We blacked out the windows with paper and cloth. I took out most of the lightbulbs and blocked the oven glass with tinfoil. Friends brought weekly groceries and essentials. I bought a small laptop to watch TV – even with that, I have to wrap up in blankets before I switch it on. I spend 18 hours a day in total darkness.

There are times when exposing myself to light is unavoidable, of course. I refuse to live without fresh air, so I go for a walk at 5am each morning, as the streetlamps are going off but before the sun has risen. If I wear a hat, hoodie and gloves, I don’t burn so much. When I go to hospital, I wrap up similarly. As soon as I arrive, they put me in a darkened room. Once, I was in there two hours. They’d forgotten about me.

At home, I have a cap with a torch attached, which I use for 15 minutes at a time – while preparing food, painting, washing. I let my beard grow. One of the advantages of living without light is you don’t have to worry too much about appearances.

Going out to socialise is impossible, but family and friends bring new people to visit. I have a dinner party every Thursday. We sit in the dark and eat, laugh, play piano. One friend said she loves coming because at my place, you don’t need to worry you might cause offence by not smiling.

In the dark on my own I listen to audiobooks or work out. I can check emails for maybe 10 minutes and I’ve set up speakers in every room and play the sounds of the rainforest all day. It’s therapeutic and helps transport me when I’m feeling trapped.

I refuse to mope. Sometimes I feel a prisoner of light – like my whole existence has been shrunk into a single apartment – and that’s more isolating than I ever imagined. But I live in hope that I’ll recover. I dream of taking a long stroll in the sun, or a trip out of the city, or really seeing my art again. But if those things never happen, I’m happy with the life I’ve had. In a way, this condition has sharpened my appreciation of the world. Every morning on my walk, it’s as if I see it afresh and its beauty never fails to take my breath away.

• As told to Colin Drury

Watch How To Make A Pearl, about John Kapellas’ past and present life, at theguardian.com/pearl

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