If you've ever sipped (chugged) any alcoholic beverage on a night out then you will be only too aware of the awful, head-thumping, headache that appears the morning after.
Your friends may tell you that a cold can of coke will cure it, your colleagues might say that a strong cup of coffee and buttery toast helps lessen the pain but that's probably because (like us) they had no idea of the quite frankly, horrifying reason behind a hangover headache.
Shona Wilkinson, head nutritionist at nutricentre.com, explained to that the key lies in the fact alcohol is a diuretic.
'This means that once it is in your blood, your body needs to put its water supplies into the blood stream to dilute it,' she says.
This, in turn, creates an increase in blood volume and pressure and the in order to lower it your body needs to get rid of water (hence why we need the loo so much when we're drunk).
But this means that our cells are now lacking the water that they need to work and so, prepare yourselves, it takes water from the brain and causes it to shrink.
'Our brain is around 70 per cent water, and dehydration can lead to brain shrinkage, which is what causes the pain,' Shona explains.
The pain you feel is your brain pulling away from the skull and triggering pain sensors leading to a headache.
We told you, horrifying.