You have a hangover. This means many things, but most importantly:
You drank alcohol.
You didn’t drink enough other fluids.
You are now dehydrated.
Get thee to a glass of water. Drink. Repeat.
Replenish your body’s fluids or you might go to bed as uncomfortable as you woke up.
Next time, try chasing those shots with some H20 instead of the icky light beer.