The ancient greeks developed the "humoral theory" with the idea that emotional and physical illness had to do with an imbalance in the 4 fluids, or "humours", found in the body.
One of the was melancholia
or "black bile
." today, we would describe this type of person as often negative, pessmistic, or depressed. It would be good for you to seek help if you find that you are often depressed.