The medical term is nausea. A feeling of sickness with an inclination to vomit
Nausea in the midst of a hangover strikes whenever you smell, taste, or even look at anything remotely related to food and beverages. A person hungover might say: I can't bear the sight of anything to eat or drink. I just feel too nauseous
wikiHow says this:
One of the main causes of nausea during a hangover is not just because
of the alcohol itself (myth), a good portion of it is the low blood
sugar ( liver using up all available glucose to process the alcohol)
and the increased stomach acid production ( especially if you drank
red wine).
Wikipedia states
An alcohol hangover is associated with a variety of symptoms that may
include drowsiness, concentration problems, dry mouth, dizziness,
gastrointestinal complaints, fatigue, sweating, nausea,
hyper-excitability, anxiety and a feeling of general discomfort