We've all been there; you wake up the morning after the night before, and you feel alright...until you actually stand up.
As the day goes on, you head starts pounding, your mouth feels like the Sahara desert and you can't stomach a single thing.
The worst part? The shakes eventually kick in and you have to make it your business to try and hold a glass of water steady.
But why do we even get the shakes after a night on the sauce?
This basically means we experience a mild version of what a drug addict may feel.
Dr O'Brien said the reason drinking alcohol when you're hungover to "cure" your hangover is because you're giving your body what it has been craving, and it therefore returns to "normal".
He said: "The hair of the dog will temporarily make you feel a bit better because some of the symptoms you are experiencing are a direct withdrawal effect."
He added: "After the first drink you feel like Superwoman; you feel brilliant, your sweats and shakes go away."
While we may feel on top of the world after a drink, any more than one will knock us right back down to where we started.
So although it may be hard, especially over the festive season, the best plan of action may be to skip the extra round of shots, and just drink a tad less in general.