I was the class jester at school in the 70s and 80s, because I wanted to be liked. The truth was that I was struggling.

I now know that I had a trio of conditions: dyslexia, attention deficit hyperactivity disorder and Irlen Syndrome, a neurological condition that makes it hard to process visual information. Words swim on the page for me; it’s difficult to see them, let alone read them. When I started school 40 years ago, no one picked this up. I just thought it was normal to see words swirling in 3D. I couldn’t understand why I couldn’t read or write like my friends, so I made a joke of it. But the joke carried on for too long.

At primary school, I created a persona: Josh. Johnny was the funny, good-looking guy whom everyone loved; Josh was the boy inside who wanted to learn, but couldn’t. When I started secondary school, a teacher made me stand on a chair and read. She wanted to show me I was stupid. It was so humiliating that I would shake, and I developed a bad stutter.

I continued to fall through the net, emotionally and educationally. Johnny the joker was doing fine – he wasn’t clever, but had lots of mates. Introvert Josh struggled. The only thing I loved was practical biology. I wanted to be a neurologist, but everyone laughed at that.

I didn’t talk to any teachers or family about this. I was clever at hiding it. When I had to write anything down, I guessed, forming what I hoped were the right words. I’d copy my friend’s work; he knew something was wrong, so let me. I cheated or guessed in tests. I became good at learning by heart.

I left school with an O-level in home economics. My big brother Ian, my idol, had joined the military, so I did, too. It was brilliant – practical and physical. I was proud of myself. I was a great soldier – I got my green beret – but I couldn’t write a report.

I also had to pretend I wasn’t gay ( it was illegal to be openly gay when I joined) so I had two big secrets for more than 12 years. I came out in my late 20s, but still couldn’t bring myself to tell anyone about the reading and writing.

In 1994, I trained to be a medic in the military. Most of the work was in the field and I relied on my team for any written work. I became quite senior, working in war zones.

But things unravelled when I did a course in pre-hospital emergency care. I had passed all my practical exams, preparing for them by learning by heart and intently watching people who were good at their job. The problem was that I’d failed the written exam. The examining doctor wanted an explanation. I was embarrassed, but told him I had dyslexia and that I couldn’t read. He urged me to get back into education. I was 34.

I applied to do a degree, biological medicine and health sciences, at the Open University. They set me up with an educational psychologist, who told me that my peer group outranked me by 15 years. Then I was diagnosed with Irlen Syndrome and finally everything made sense.

It was back to basics on the course. I knew the alphabet and some words, but my vocabulary was small. Using my Disabled Students’ Allowance, I paid for a tutor, who worked with me every week, teaching me to understand words through pictures. It was a bit childish, but it worked. I had a laptop with read-and-write and speak-and-spell programs. Reading material was printed on green paper to help with the Irlen Syndrome – the colour helps my brain correct the distortion. The tutor would look over my OU work, advising me on grammar and spelling mistakes.

It took nine years to get that degree – something I had never dreamed of. Now, aged 47, I’m an ambassador for the OU; this year I won an award in recognition of the way I’ve embraced education later in life. I now teach pre-hospital emergency care to doctors, nurses, medics and paramedics. I also teach children and adults with learning difficulties, because I want to give others the chances I had.

I still struggle to read a menu if I’m not wearing my tinted glasses, but luckily my fiance, Alexandro, is usually on hand to help. I look back and wonder how many other people have struggled with education and where they are now. I’m proof that no one should be discounted, ever.

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