Possibly The Most Misunderstood Condition, Fibromyalgia
If you look at someone suffering from fibromyalgia, you would probably not even know it. Most people with this condition look perfectly normal on the outside. On the inside is a whole different story. Their skin or muscles may feel like they are on fire, or just ache, as if they were bruised. Most can't sleep a full night and after a while, this all takes its toll.
Here is a video called Fibromyalgia 101, that really sheds some light on this condition: