Dehydration and Electrolyte Imbalance
The increased urine production, sweating, vomiting, and diarrhea that alcohol consumption causes dehydrates the body. This causes many common hangover symptoms such as thirst, weakness, dry mouth and nose, dizziness, and lightheadedness.

Gastrointestinal Disturbances
Excessive alcohol consumption can irritate the stomach and intestines, causing inflammation of the stomach lining (gastritis), delayed stomach emptying. Chemicals secreted by the pancreas and intestines can cause abdominal pain, nausea, and vomiting.

Low Blood Sugar
Alcohol consumption can inhibit glucose production and deplete glucose reserves stored in the liver. Because glucose is the brain’s main energy source, low blood sugar contributes to the fatigue, weakness, and mood disturbances of hangovers.

Disruption of Sleep and other Biological Rhythms
Alcohol-induced sleep is usually of shorter duration and poorer quality than normal sleep, causing fatigue. Alcohol also can disrupt the body’s daily temperature rhythm, nighttime secretion of growth hormones, and cortisol release, all of which can produce symptoms akin to jet lag.

Alcohol intoxication causes widening of blood vessels (vasodilation), which can cause a headache. Alcohol consumption also affects the production of histamine, serotonin, and prostaglandins—hormones thought to contribute to headaches.

Alcohol Withdrawal
Heavy drinking depresses the central nervous system. When alcohol is withdrawn, it can go into an unbalanced hyperactivity state. This can cause the tremors and rapid heartbeat associated with hangovers. Many of the signs and symptoms of hangover overlap the symptoms of alcohol withdrawal syndrome.

Effects of Alcohol Metabolites
In your body, alcohol dehydrogenase (ADH) and aldehyde dehydrogenase (ALDH) break alcohol molecules down so they can be eliminated. Alcohol is metabolized by ADH to acetaldehyde, which is then broken down further into acetate. Some people have genetic variants of ALDH that allow acetaldehyde to accumulate and cause toxic effects. Although acetaldehyde is no longer in the body when the blood alcohol level reaches zero, its toxic effects can persist into the hangover period, researchers believe.

These symptoms vary from person to person and can range in intensity from mild to severe. Sometimes, they’re enough to derail your entire day.

Hangovers tend to go away on their own, usually within 24 hours.