I tend to refer to a hangover as "interdose withdrawal".
Aside from the dehydration, mineral deficiency and alcohol metabolites; your GABA system is reeling from the lack of alcohol, hence the sensitivity to loud noises, bright lights etc. Having another drink (if you rehydrate yourself too) usually fixes all the problems right away.
Withdrawal on the other hand is permanently removing the outside substance and thus forcing your body to use no longer correctly functioning systems in place of the alcohol. The body will slowly attempt to correct the broken systems, reintroducing alcohol simply stops that correction process.
So a hangover and withdrawal are one and the same thing, just the severity differs.