1
general::
The unpleasant results of an earlier activity, especially overindulgence in alcohol. For example, A headache is just one of the symptoms of the morning after. This expression originated in the late 1800s as a synonym for a hangover (and was often put as the morning after the night before). By the mid1900s, however, it was Also being used more loosely for the aftereffects of staying up late.
American Heritage Idioms