Invisible disability can be so hard to explain. I find it can be a good idea to almost get a bit of a script going to help explain it to people in a way that doesn't make them think 'its all in your head' which we all know it's not and only recently being proven :) its hard work finding a script or default answer that works for you and will take a bunch of revising but I find explaining auto immune response in a lay way can often be good. Just letting people know depending on your symptoms what your boundaries are and how people can respect them whether that's about unsolicited touching etc. I would also add that some people are never going to understand or be emphatic or be able to accommodate your needs and that's ok too it's not on you and can be hard to navigate and understand when it's worth your energy or time. Something I'm continuously trying to work on. Hope that's not too rambly and makes sense!

If someone is truly interested I will explain the symptoms, but I do not really go into any type of detail if they are not truly interested.
Sometimes when explaining, I find The Spoon Theory helpful. It is a wonderful story about a woman who explains the effects of chronic illness to her friend. I hope it helps. This is the link: https://butyoudontlooksick.com/articles/written...

Mostly had this trouble since becoming a fibro sufferer which is nearly 15yrs. No one really knows unless your a sufferer! They may care & understand but will never know.

On the topic of "why explain to others"...I've noted on this site that some people with fm become very isolated. An unwillingness to try with others could make for a very lonely existence. It's good to be mindful of the little steps that lead us to a life we don't like or want.

A prepared script is a good idea. I say I have "arthritis issues ", bit of a cop out I know, but that's a visible symptom because I often limp or move slowly.