What is an invisible disability?

 There are many conditions that are terribly debilitating and life destroying yet don't manifest any visual signs that others would identify as an illness or disability just by looking at you. They include autoimmune conditions (like lupus and hashimotos), mental health conditions (such as depression, OCD and Bipolar), chronic pain conditions (like CRPS, EDS, fibromyalgia, dysautonomia, etc), respiratory conditions (such as asthma, cystic fibrosis, etc) and heart conditions to name just a few. People who suffer from these illnesses, despite looking healthy on the outside most of the time, can be severely restricted and disabled by their symptoms.