Expressing chronic pain is like trying to show emotion without a face. It does not matter how hard you try, people will still not understand that just because it does not show, it does not mean it is not there.
Chronic pain IS underestimated, and it affects so many people. Awareness is key. I was diagnosed with fibromyalgia and reflex sympathetic dystrophy at both of which have thankfully been in remission for the most part.