Hangover symptoms typically begin when your blood alcohol content drops significantly and is at or near zero. They're usually in full effect the morning after a night of heavy drinking. Depending on what and how much you drank, you may notice:

• Fatigue and weakness
• Excessive thirst and dry mouth
• Headaches and muscle aches
• Nausea, vomiting or stomach pain
• Poor or decreased sleep
• Increased sensitivity to light and sound
• Dizziness or a sense of the room spinning
• Shakiness
• Decreased ability to concentrate
• Mood disturbances, such as depression, anxiety and irritability
• Rapid heartbeat

Hangovers are caused by drinking too much alcohol. A single alcoholic drink is enough to trigger a hangover for some people, while others may drink heavily and escape a hangover entirely.

Various factors may contribute to a hangover. For example:

• Alcohol causes your body to produce more urine. In turn, urinating more than usual can lead to dehydration — often indicated by thirst, dizziness and lightheadedness.
• Alcohol triggers an inflammatory response from your immune system. Your immune system may trigger certain agents that commonly produce physical symptoms, such as an inability to concentrate, memory problems, decreased appetite and loss of interest in usual activities.
• Alcohol irritates the lining of your stomach. Alcohol increases the production of stomach acid and delays stomach emptying. Any of these factors can cause abdominal pain, nausea or vomiting.
• Alcohol can cause your blood sugar to fall. If your blood sugar dips too low, you may experience fatigue, weakness, shakiness, mood disturbances and even seizures.
• Alcohol causes your blood vessels to expand, which can lead to headaches.
• Alcohol can make you sleepy, but it prevents deeper stages of sleep and often causes awakening in the middle of the night. This may leave you groggy and tired.

Congeners

Alcoholic beverages contain ingredients called congeners, which give many types of alcoholic beverages their flavor and can contribute to hangovers. Congeners are found in larger amounts in dark liquors, such as brandy and bourbon, than in clear liquors, such as vodka and gin.

Congeners are more likely to produce a hangover or increase the severity of a hangover. But drinking too much alcohol of any color can still make you feel bad the next morning.

Anyone who drinks alcohol can experience a hangover, but some people are more susceptible to hangovers than others are. A genetic variation that affects the way alcohol is metabolized may make some people flush, sweat or become ill after drinking even a small amount of alcohol.

Factors that may make a hangover more likely or severe include:

• Drinking on an empty stomach. Having no food in your stomach speeds the body's absorption of alcohol.
• Using other drugs, such as nicotine, along with alcohol. Smoking combined with drinking appears to increase the likelihood of next-day misery.
• Not sleeping well or long enough after drinking. Some researchers believe that some hangover symptoms are often due, at least in part, to the poor-quality and short sleep cycle that typically follows a night of drinking.
• Having a family history of alcoholism. Having close relatives with a history of alcoholism may suggest an inherited problem with the way your body processes alcohol.
• Drinking darker colored alcoholic beverages. Darker colored drinks often contain a high volume of congeners and may be more likely to produce a hangover.

When you have a hangover, you're likely to experience problems with:

• Memory
• Concentration
• Dexterity

Not surprisingly, this temporary dulling of your abilities increases your risk of a number of problems at school or work, such as:

• Absenteeism
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• Trouble completing tasks
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• Conflict with others
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• Falling asleep at school or on the job
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• Workplace injuries
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