Merriam-Webster Collegiate Dictionary - sleeping sickness

 noun  Date: 1875  1. a serious disease that is prevalent in much of tropical Africa, is marked by fever, headache, lethargy, confusion, and sleep disturbances, and is caused by either of two trypanosomes (Trypanosoma brucei gambiense and T. b. rhodesiense) transmitted by tsetse flies  2. any of various viral encephalitides or encephalomyelitides of which lethargy or somnolence is a prominent feature