The Spoon Theory
I explained that the difference in being sick and being healthy is having to make choices or to consciously think about things when the rest of the world doesn’t have to. The healthy have the luxury of a life without choices, a gift most people take for granted.
Most people start the day with unlimited amount of possibilities, and energy to do whatever they desire.
– Christine Miserandino, But You Don't Look Sick

Invisible Illnesses ..

.. are the hardest for others to understand. And although this piece is written about Lupus, it does a good job of explaining what it's like to live with an illness that restricts the resources available to you. My context is depression, anxiety and such.