Fatigue

Fatigue is a persistent sense of tiredness or lack of energy that is not fully explained by exertion and is not fixed by ordinary rest.

It differs from sleepiness, which is a drive to fall asleep, and from muscle weakness, which is a measurable loss of strength. Fatigue is a symptom rather than a diagnosis and accompanies many conditions, including insufficient sleep, anemia, thyroid disorders, depression, chronic pain, infection, autoimmune disease, cancer and its treatment, and medication effects. In pets it appears as lethargy, reduced play and reluctance to exercise, and can signal illness that needs veterinary attention.

Assessment starts with a history that separates fatigue from sleepiness and weakness, reviews sleep, mood, activity and medications, and is followed by physical examination and basic blood tests. Questionnaires such as the Fatigue Severity Scale grade how much it interferes with daily life. When fatigue lasts six months or more without another explanation, clinicians consider myalgic encephalomyelitis/chronic fatigue syndrome. Cannabinoids have not been studied for fatigue as such, and the symptom is one of the more commonly reported effects of higher-dose cannabinoid use.