Fatigue, asthaenia and lack of energy are very non-specific complaints. It should be investigated whether there are any associated symptoms, such as depression, dyspnoea, fever, pain, anorexia, muscle weakness, weight loss, etc. Fatigue occurring after minor exertion is more likely to be of organic origin than a feeling of fatigue that is already present in the early morning. A number of possibilities that may or may not be connected with travel are given below. A problem that occurs during or after a trip does not necessarily need to have a causal connection with that trip.

Fatigue after a trip to distant places is a frequent occurrence. Various factors are involved here:

• Many trips are stressful in itself, rather than relaxing, something that is frequently overlooked.
• Jet-lag on journeys in an east-west direction (not on north-south journeys). Daytime drowsiness and insomnia at night improve after a few days (depending on the number of time zones crossed).
• Physical hardships (especially on long low-budget journeys).
• Various self-limiting infectious and organic problems (from hyponatraemia to side effects of medication). These causes are usually obvious from the general context.
• Cardiac and pulmonary problems on trips at high altitudes (Andes, Himalaya mountains). There is certainly a definite risk for individuals with a pre-existing limited cardio-respiratory reserve. The complaints usually quickly disappear after return to low-lying areas.
• Psychological problems of readaptation to the Western lifestyle with its problems of stress and high work rhythm.

Here we differentiate a number of causative categories:

• Active infections: e.g. hepatitis A, B, C, D, E, chronic malaria, kala azar, brucellosis, legionellosis, Q fever, trypanosomiasis, tuberculosis, AIDS. Chronic gastroenteritis and "smoldering malaria" are frequent causes.
• Post-infection fatigue. The convalescence phase of various infectious diseases, such as mononucleosis, Q-fever, dengue, leptospirosis, hepatitis A, B, C, E, cytomegalovirus infection and toxoplasmosis, are often characterised by persistent asthaenia.
• Side effects of medications, such as beta-blockers or sedatives. A vacuolating myopathy due to chloroquine can occur after prolonged use of this medicament. Borderline or cryptic myasthaenia gravis can be aggravated by chloroquine. Zidovudine (Retrovir®) can also be associated with myositis and muscle weakness.
• Sleep apnoea syndrome. The patient’s sleep is profoundly disturbed by repeated attacks of apnoea resulting from intermittent obstruction of the upper airways. Poor quality of sleep will cause pronounced fatigue and drowsiness during the day. A partner’s heavy snoring may be part of the problem. The opinion of an otorhinolaryngologist should be obtained. A polysomnography is necessary.
• Hypotension with or without salt depletion (sodium / potassium loss due to diarrhoea and prolonged sweating). This is often obvious from case history.
• Endocrine problems. Bites by a Russell’s viper (India and Southeast Asia) are often complicated by haemorrhages and destruction of the pituitary gland, with panhypopituitarism as a result (comparable with Sheehan syndrome post-partum). Addison syndrome is another complication. This can also occur through the adrenal glands being affected by tuberculosis or by histoplasmosis. Hypo- and hyperthyroidism usually pose no diagnostic problems. Hyperthyroidism due to Basedow's disease can occur through prolonged use of iodine for water disinfection. Certain areas have a high prevalence of goitre, due to iodine deficiency and of the presence of substances in the diet that interfere with iodine uptake (goitrogens, cassava). This is however a problem for the local population and not for the tourist. Diabetes mellitus can of course also cause fatigue.
• Various organic abnormalities, such as anaemia, autoimmune diseases, neoplastic disorders, organ failure (heart, lung, liver or kidney failure) can result in asthaenia. Substantial hypokalaemia is accompanied by muscle weakness. Neurological diseases such as myasthaenia gravis, Eaton-Lambert syndrome and muscle diseases, including muscular dystrophy and myositis (trichinosis, sarcocystosis, polymyositis) should be considered. Multiple sclerosis and Parkinson’s syndrome can be accompanied by pronounced fatigue.
• Psychological problems, such as depression and alcohol abuse. Brucellosis, neurosyphilis and trypanosomiasis can manifest themselves as a depression. Psychic decompensation can be due to culture shock and by the practical problems encountered on long journeys. Some people undertake a long journey as a psychological escape from personal problems in their own country and situation (relationship problems, stress). Confrontation with loneliness and uncertainty in foreign environments can make these problems even worse. Unexpressed fear of infection (e.g. AIDS) or guilt feelings (e.g. sex tourism) can be expressed as fatigue. Side effects of medication such as mefloquine, tend to disappear rather quickly after the offending medication is stopped.
• The "chronic fatigue syndrome" is a poorly understood entity, without pathognomonic characteristics. It is probably caused by a mixture of different entities.