WordNet (r) 3.0 (2006):

sleeping sickness
    n 1: an encephalitis that was epidemic between 1915 and 1926;
         symptoms include paralysis of the extrinsic eye muscle and
         extreme muscular weakness [syn: sleeping sickness,
         sleepy sickness, epidemic encephalitis, lethargic
         encephalitis, encephalitis lethargica]

Moby Thesaurus II by Grady Ward, 1.0:

145 Moby Thesaurus words for "sleeping sickness":
   African lethargy, Asiatic cholera, Chagres fever, German measles,
   Haverhill fever, acute articular rheumatism, ague, alkali disease,
   amebiasis, amebic dysentery, anthrax, bacillary dysentery,
   bastard measles, black death, black fever, blackwater fever,
   breakbone fever, brucellosis, bubonic plague, cachectic fever,
   catalepsy, cerebral rheumatism, chicken pox, cholera, coma, cowpox,
   dandy fever, deer fly fever, dengue, dengue fever, diphtheria,
   dumdum fever, dysentery, elephantiasis, encephalitis lethargica,
   enteric fever, erysipelas, famine fever, five-day fever, flu,
   frambesia, glandular fever, grippe, hansenosis, hepatitis, herpes,
   herpes simplex, herpes zoster, high, histoplasmosis, hookworm,
   hydrophobia, infantile paralysis, infectious mononucleosis,
   inflammatory rheumatism, influenza, jail fever, jungle rot,
   kala azar, kissing disease, lepra, leprosy, leptospirosis,
   lethargy, loa loa, loaiasis, lockjaw, madness, malaria,
   malarial fever, marsh fever, measles, meningitis, milzbrand, mumps,
   narcohypnosis, narcolepsy, narcoma, narcosis, narcotic stupor,
   narcotization, nod, ornithosis, osteomyelitis, paratyphoid fever,
   parotitis, parrot fever, pertussis, pneumonia, polio,
   poliomyelitis, polyarthritis rheumatism, ponos, psittacosis,
   rabbit fever, rabies, rat-bite fever, relapsing fever,
   rheumatic fever, rickettsialpox, ringworm, rubella, rubeola,
   scarlatina, scarlet fever, schistosomiasis, sedation,
   septic sore throat, shingles, shock, sleepy sickness, smallpox,
   snail fever, sopor, splenic fever, spotted fever, strep throat,
   stupor, swamp fever, swoon, tetanus, thanatosis, thrush, tinea,
   trance, trench fever, trench mouth, tuberculosis, tularemia,
   typhoid, typhoid fever, typhus, typhus fever, undulant fever,
   vaccinia, varicella, variola, venereal disease, viral dysentery,
   whooping cough, yaws, yellow fever, yellow jack, zona, zoster