There are many sufferers of Fibro, Chronic Fatigue, Epstein Barr and while progress has been made there is still a lot of ignorance and misunderstanding about it, even by the best intentioned.
I am one of the fortunate. I can be laid low in pain and suffering and know it will pass. For many the passing never occurs and is constant. If you know someone who suffers learn as much as you can by it. Understanding is the best support.
This me six years ago. It still happens a couple of times a year but many are worse.
bridgesburning 
I’ve met many a people who share the same sentiment. Knowing others don’t understand makes them feel even worse.
Its true that pain is not something that always shows like a cold would and most people assume if they can’t see it it isn’t there.
Take care friend. By now you know when your unwelcome friend visits you have to lie down and take it easy.
I will….have been doing well. Hope this day is as productive as yesterday sounded for you!