One of the aspects of hangover is the disorientation and dizziness. The reason for this aspect of the hangover is quite simple, the density of the fluid in the inner ear (the semicircular canals) which helps us maintain our equilibrium and balance has changed from when we last remember it. This is because alcohol (having a different density than the normal fluid) has entered the canals.

When getting drunk it is a gradual process that we often are not aware of. It is the awakening the next day where the fluid is back to normal and we last remember it in our most intoxicated state that things get confusing.

Having the "hair of the dog" restores the liquid to a density more similar to what was last remembered which is then gradually purged from our system and the balance gradually returns to normal. Drinking a Bloody Mary ora a Red Eye are often prefered forms of the dog.