I was recently on a packed Central line train into London. Luckily, I managed to take the last priority disabled seat. My osteoporosis and the fatigue I experience meant it would be hard for me to stand for the 40-minute journey to Oxford Circus. I felt a sense of relief that I had managed to find a space. That was until I was approached by a middle-aged woman, who quite confidently asked me to move in order to give up my seat for an elderly passenger.

Of course, I thought, the elderly passenger deserves a seat. But I do too, although it’s not immediately obvious why. With other passengers shaking their heads and murmuring comments of disapproval, and me too embarrassed to make a claim for the seat, I moved. It’s true that I appear well, but standing for a prolonged period of time left me feeling weak and in pain. That said, I am used to keeping quiet.

Invisible illnesses come in many different forms, from arthritis to ME and Crohn’s disease. They present themselves with varying degrees of severity and a wide range of symptoms, including chronic pain, weakness and mental health problems. Despite being a constant presence in our lives, they are not obvious to the onlooker.

I was six when I was diagnosed with cystic fibrosis, a chronic condition that affects the lungs and digestive system. It is caused by a defective gene that allows secretions to block passageways in the lungs and pancreas. It also affects bones, the liver, sinuses and fertility. Despite my rigorous daily treatments – which take up to three hours – regular hospital admissions, the huge list of other diagnoses it comes with and a shortened life expectancy, I do not look ill.

Of course, there are some obvious benefits to looking healthy. It can give people with illnesses control over how much of them we share with others; it allows us to go about much of our daily lives without facing certain kinds of prejudice and discrimination. Knowing someone has a disability more often than not changes the way you perceive them. Whether the reaction is discriminatory or empathetic, this unwanted attention can make life feel suffocating. In being open about our disability, we unfortunately have to accept the reality that people will treat us differently.

Next time you see someone sitting in a priority space, remember there is often more to a situation than meets the eye

Even so, it’s clear there is a need to raise awareness of the existence and legitimacy of invisible illnesses. Using disabled facilities as a young person who appears to be well leaves me feeling stressed and ashamed: in the past, people have told me I shouldn’t be using the disabled toilets when in public places, as I “don’t look ill”. This, to them, means I can’t be disabled.

But we need to get better at recognising not all illnesses are obvious at first sight. More often than not I have felt I have to prove I am ill in order to get access to services I deserve; this leads to a feeling of isolation and even fear about going out. Schemes such as the “please offer me a seat” initiative on the underground are a step forward, as they give those living with invisible illnesses confidence that passengers will accommodate their needs, while avoiding the need to “prove” their disability to strangers.

Blue badges are also being extended to those with hidden disabilities. But having the law on your side isn’t the whole solution. Getting into trouble for using a disabled parking space because you “look fine” is a traumatic experience some of my friends with cystic fibrosis have been through and it’s the main reason I still haven’t applied for my badge, despite having had the right to do so for years.

Ultimately, more efforts to educate the public need to be made at a national level, with schools teaching children about the wide range of disabilities. For the moment, people with hidden disabilities need to talk about their conditions and stand up for their right to access services and facilities. That’s easier said than done, of course. So next time you see someone sitting in a priority space on the train or leaving a disabled toilet, remember there is often more to a situation than meets the eye.

• Isabelle Jani-Friend is a recent graduate of the University of Southampton