Medicine. A physical state of sluggishness, apathy (indifference), inattention and/or reduced physical activity, usually from illness, overwork or chemical exposure. Lethargy may also be described as stupor, severe drowsiness, severe fatigue, exhaustion, or weariness. A lethargic person lacks energy and feels unwilling and/or unable to do anything. Additional Info: Chronic fatigue syndrome is a poorly understood condition of fatigue or "mind fog" that persists for months or years. It is marked by: (1) Severe chronic fatigue lasting six months or longer with no other known underlying medical cause and; (2) Four or more of the following symptoms: substantial impairment in short-term memory or concentration, sore throat, tender lymph nodes, muscle pain, multi-joint pain without swelling or redness, headaches of a new type, pattern or severity, unrefreshing sleep, and post-exertional malaise lasting more than 24 hours. The causes of chronic fatigue syndrome are not well understood. Chemical exposure is not believed to be a cause. MSDS Relevance: Lethargy or drowsiness may be a symptom ofacute (short-term) exposure to certain chemicals. Inhalation of vapors or gases is a common cause of lethargy. Lethargy can dull the victim's awareness of the danger, and he may fall asleep or become unconscious before being able to act. If the victim is not removed to fresh air, continued exposure could result in system injuries, coma, and death. A particularly dangerous example of a chemical that causes lethargy at relatively low concentrations is carbon monoxide. See also: Malaise, Prostration, Stupor, Syncope