Fatigue is a subjective feeling of tiredness that has a gradual onset. Unlike weakness, fatigue can be alleviated by periods of rest. Fatigue can have physical or mental causes. Physical fatigue is the transient inability of a muscle to maintain optimal physical performance, and is made more severe by intense physical exercise. Mental fatigue is a transient decrease in maximal cognitive performance resulting from prolonged periods of cognitive activity. It can manifest as somnolence, lethargy, or directed attention fatigue.Medically, fatigue is a non-specific symptom, which means that it has many possible causes and accompanies many different conditions. Fatigue is considered a symptom, rather than a sign, because it is a subjective feeling reported by the patient, rather than an objective one that can be observed by others. Fatigue and ‘feelings of fatigue’ are often confused.
Drowsy or sleepy.
Causing literal or figurative sleepiness; soporific.