A hangover is mainly caused by drinking too much alcohol. It happens because alcohol and its breakdown products affect several parts of the body, including the stomach, brain, immune system, and sleep cycle.

What causes it

  • Alcohol is broken down into a toxic byproduct called acetaldehyde , which can contribute to headache, nausea, and feeling unwell.
  • Alcohol can increase urination and may leave you dehydrated, which can worsen thirst, dry mouth, and fatigue.
  • It can irritate the stomach and increase acid production, leading to nausea or vomiting.
  • It disrupts sleep, so you may feel extra tired and foggy the next day.
  • Inflammation and early alcohol-withdrawal effects can also play a role in symptoms like headache, weakness, and irritability.

Why it feels worse

Hangover severity depends on how much you drank, how fast you drank, whether you ate food, and even the type of alcohol. Darker drinks often have more congeners, which can make hangovers worse for some people.

When to worry

Most hangovers improve with time, but severe symptoms can signal alcohol poisoning, which is a medical emergency. Warning signs include confusion, slow or irregular breathing, repeated vomiting, or trouble staying awake.

Quick takeaway

So, in plain terms: a hangover is your body reacting to too much alcohol, especially its toxic breakdown products, dehydration, stomach irritation, poor sleep, and inflammation.