To look at me, you wouldn't guess that I am disabled. I'm a strapping ex rugby player, 5ft 10in tall. But beneath my skin, my bones tell a different story. They are liable to fracture or break at the slightest knock. At 50, I have the bones of an 80-year-old.

My sudden physical deterioration occurred seven years ago. I'd taken my wife, Jean and our daughter, Lauren, then four, on a surprise holiday to the Dominican Republic to celebrate our first wedding anniversary. One evening out, I found myself being dragged on to the stage to take part in a ballroom dancing competition with Jean. I'd never been much of a dancer, but it seemed churlish not to take part. Halfway through the performance, I felt a giant blow to the middle of my back, accompanied by a noise which, to me, was as loud as a gunshot. Had someone struck me with a sledgehammer? Shot me? I turned around to check, but all I saw was the audience clapping and cheering. I managed to stagger to the back of the stage where I promptly passed out.

When I came round a couple of minutes later, the curtains on the stage had been drawn and a crowd of people had gathered around me. They all thought I'd had a heart attack, but Jean knew it was my back. She told me later that she had felt it shatter as she clung on to my shoulders during the dance.

I had no feeling in my legs and the bits of my body that I could feel were in agony. As we waited for help, I tried to calm myself that it was probably a trapped nerve.

There's nothing that makes you appreciate the NHS more than falling ill in a less-well-off country. The "ambulance" was more like a minibus with a light on top. They didn't even have a stretcher so the paramedics had to roll me on to a sun lounger that they had swiped - I would have laughed if I hadn't been in so much pain.

After I'd been x-rayed at the hospital, I overheard one of the doctors say that my back was broken so badly, it was as if I'd fallen three storeys. I had just 25% of my vertebrae left. A week passed before I was deemed fit enough to fly home. During that time I remember crying down the phone to my boss and wondering whether I'd ever walk again.

Back in the UK, I had test after test to try and establish what had caused my back to shatter without warning. Doctors initially suspected cancer, but the tests came back negative. Meanwhile, I was still in pain, wondering if I was going to be able to walk my daughter down the aisle and, in my bleakest moments, whether I'd even live to see her get married. My pain was made worse by not knowing what had caused it.

Four months after my collapse, I had major surgery to replace my damaged spine with a titanium cage. For two months afterwards, I had to lie flat on my back. Even to cough was agony. It was during my recovery that I finally got my diagnosis. I was suffering from severe spinal osteoporosis. The doctor told me it was one of the worst cases that he had ever seen.

What he didn't go on to explain was that once your body deteriorates into old age, so does your lifestyle. I had to take early retirement from my job as a sales director. I was used to travelling up and down the UK, meeting new people. Now my world was confined to the living room. I couldn't even go to bed at night because it hurt my back to lie flat. I spent my days and nights in a reclining chair, staring at the TV or doing crosswords. It was as if time had rushed ahead of me somehow, wiping out 40 years of my life and rejoining me again as an old man. It didn't help that there was no one I could talk to who really understood what I was going through. As osteoporosis is more prevalent in women, all the literature about it was geared towards them.

Jean was supportive, even giving up her job as a hairdresser to be with me, but I resented having to rely on her. Before the accident I had taken pride in being able to provide for my family. My pride had shattered along with my back. I'd sit in my chair for days on end without speaking. Aside from losing three inches in height, my illness hasn't changed my physical appearance. Because of this people find it difficult to grasp how weak I really am. I felt that if I smiled or chatted then people would think I was OK and not realise the constant pain I was in.

Eventually, I went to see a doctor and was diagnosed with clinical depression. He referred me to a psychologist who taught me how the mind can be a wonderful tool in pain reduction. Feeling happy and relaxed can make the world of difference.

At first, changing my outlook seemed easier said than done. I was once a happy-go-lucky sort of person, but now I had to remind myself even to smile. Gradually, though, I pulled myself out of the cycle of self pity and put a brave face on instead. I started to do voluntary work for the National Osteoporosis Society. Three years ago, I was chosen to be an ambassador for the charity. It's an achievement that's given me back some of my shattered pride.

One of the saddest things is that I no longer see any of my six brothers and sisters. Their way of dealing with my illness is to ignore it and me. Friendships have fallen by the wayside too. When the ones that have stuck around come to see me, I don't tell them how I really feel when they ask. I've learned that people just want to hear that you're fine. I'm not bitter; I accept that it's the way people are.

I try not to think: why me? The exact cause of osteoporosis is unknown. What is known is that one in two women and one in five men over the age of 50 will fracture a bone, mainly as a result of osteoporosis. I'll never understand why it struck me so hard, so young, but I'm determined not to let it ruin my life. My body may be twice the age it should be, but my mind, at least, is as strong as ever ·

• Robert Rees was talking to Danielle Wrate

• The National Osteoporosis Society can be reached at nos.org.uk, or by calling 0845 450 0230