Cognitive effects include poorer performance on mental tasks and concentration; dizziness, nausea, insomnia, confusion, anxiety, increased fatigue, headaches, and irritability; and problems with digestion, including indigestion, changes in the frequency and consistency of bowel movements, and reduced appetite.

Travel fatigue can occur without crossing time zones, and it often disappears after one day accompanied by a night of good quality sleep.

[8] Jet lag is a chronobiological problem,[11] similar to issues often induced by shift work and circadian rhythm sleep disorders.

A ten-hour flight between Europe and southern Africa does not cause jet lag, as the direction of travel is primarily north–south.

A four-hour flight between Miami, Florida, and Phoenix, Arizona, in the United States may result in jet lag, as the direction of travel is primarily east–west.

It is hypothesised that peripheral oscillators respond to internal signals such as hormones, food intake, and "nervous stimuli".

[16] This internal biological de-synchronisation is exacerbated as the body is not in sync with the environment – a double desynchronisation, which has implications for health and mood.

[20] The US Centers for Disease Control and Prevention (CDC) recommends mobile apps for the correct timing of light exposure and avoidance, when to use caffeine, and when to sleep.

[26] In the case of short duration trips, jet lag may be minimised by maintaining a sleep-wake schedule based on the originating time zone after arriving at the destination, but this strategy is often impractical in regard to desired social activities or work obligations.

[27] Shifting one's sleep schedule before departure by 1–2 hours to match the destination time zone may also shorten the duration of jet lag.

[30][31] In a study, zolpidem improved sleep quality and reduced awakenings for people travelling across five to nine time zones.

[32] The potential adverse effects of hypnotic agents, like amnesia and confusion, have led some doctors to advise patients to test such medications prior to using them for treating jet lag.

When travelling across time zones, there is a "phase-shift of body temperature, rapid-eye-movement sleep, melatonin production, and other circadian rhythms".

[37] Although significant circadian rhythm disruption has been documented as affecting individuals with bipolar disorder, an Australian team studied suicide statistics from 1971 to 2001 to determine whether the one-hour shifts involved in daylight saving time had an effect.