I love watching House, but I hate knowing about those mysterious rare diseases which could afflict me. I just watched the two-part episode from season 2 where Foreman was afflicted by Naegleria.

From Wikipedia:

Naegleria fowleri (also known as the brain eating amoeba) is a free living amoeba typically found in warm fresh water, from 25-35 degrees Celsius (77-95 degrees Fahrenheit) in an amoeboid or temporary flagellate stage. It belongs to a group called the Percolozoa or Heterolobosea.

N. fowleri can invade and attack the human nervous system; although this occurs rarely, such an infection will nearly always result in the death of the victim.

Well, I'm never stepping into warm fresh water again.

(Looks shiftily at my aquarium, which is set at 79 degrees Fahrenheit...)