Lassitude (Lethargy)

A feeling of weakness or weariness, also known as fatigue, tiredness, exhaustion, and weariness.

Persons most commonly affected: All age groups and both sexes.
Organ or part of body involved: Whole body system.
Symptoms and indications: A feeling of extreme tiredness or exhaustion, often involving muscle weakness, that can result in difficulty performing tasks. All the person wants to do is sleep.
Causes and risk factors: May be due to many causes, such as illness, depression, joint and muscle pain, stress, overextending yourself, poor sleep, anemia, or a lack of physical activity.