5. Lupus
When lupus was first discovered in the 19th century the doctors at the time originally classified it as a skin disease due to the rash that it comes with. It retained its classification for quite some time until medicine advance far enough to learn more about its true nature.
We now know that lupus actually affects multiple organs, not just the skin. This includes the heart, brain, kidneys, and joints. Seeing as lupus targets so many areas of your body, it should come as no surprise that the symptoms it will bring are just as diverse. The most common symptoms for those who suffer from lupus are fatigue, rashes, and joint pain.
Lupus is a condition that leads to hyperactivity in the immune system of the host which leads to its attack on perfectly healthy cells. The self-destructive nature of the disease is what makes its symptoms so severe. In a way, lupus is like mankind, destroying its host despite knowing that it will die along with it.