Imagine if you had an illness which left you with scales all over your neck and arms whenever you travelled. These scales are itchy, they stop you from sleeping, they distract you so you can't concentrate, and they make you feel really shit.

Imagine your friend's concern as they started appearing each time you got to your destination. Imagine how they'd approach a visit from you, checking to see if there was anything they could do to limit the impact of your disease. If you were going on holiday with a friend, imagine how the conversations about your destination would go, making sure that any environmental factors that impacted the severity of your skin issue would be discussed and together you'd choose somewhere that would make it as easy as possible for you.

Think about how this would affect any trips you take and the steps you and your travelling companions would take to limit it. Your friends wouldn't forget about it as the reminder is there for them as soon as you arrive.

Now imagine that you have this same illness, but it's invisible. And say that it affects you insidiously, such as preventing you from sleeping, not enough for you to stomp around the house and keep others awake, but enough so that you don't really get any rest, so that you have pains in your chest from the tiredness during the day, so that you feel like you haven't really slept at all, so that you can't really take on anything remotely cognitively challenging, and simple things become difficult and painful to do.

Imagine that this takes up such a huge part of your headspace when you're travelling that you can't concentrate on having fun, that the exciting things you do on holiday become overwhelming efforts and all you want to do is hide in your room. Imagine that you tell your friends that you're just tired and need to chill out, and they think that you've just had a rough night's sleep, make you a coffee and start talking about the amazing things you're all going to do that day.

Imagine all the differences between your bright red scaly disease that invites sympathy and comment, and the silent, quiet, invisible one that you mainly suffer alone.