An invisible illness is defined as any medical conditional that isn’t easily visible to others. This includes chronic physical conditions such as arthritis, diabetes, fibromyalgia, and Functional Neurological Disorder, which is what I have. It also includes mental illnesses. As you appear to be fine on the outside, people don’t understand you are really ill. This leads to frustration from the person ill and those around them. Add to this, my symptoms vary in their severity from day, week or month. Someone might see me “looking fine” so not understand why I then have cancel plans, for example. So this is how I explain my invisible illness and why.