Ever had a hangover after a night on the town? The symptoms you experienced once your blood alcohol level returned to normal, like nausea, a pounding headache, dehydration, and fatigue, were just the tip of the iceberg. New research shows that a hangover also causes a big drop in cognitive ability. 

Psychologist Dr. Lauren Owen tested the thinking and reasoning skills of volunteers before and after a night of drinking. The result: Hangovers temporarily reduced the size of the brain’s working memory by about ten percent which slowed their ability to process information, including language and spatial relationships, which affects things like driving. 
Another discovery: People with hangovers also made 30-percent more errors than teetotalers. Which means, 20-year olds who partied the night before a test had the reaction times of someone twice their age. 
And the research totally demolished one myth: The belief that hangovers get worse as you get older. The truth is older people tend to have fewer hangovers because they’ve learned their limits and drink a lot less or have given up alcohol altogether.