Sorry to be pedantic but a hangover is not just extreme dehydration, it is a toxic reaction as well. Remember the pressure your poor liver is under to remove the toxic alchohol and other poisonous ingredients. It is true that clear drinks are better than dark ones. Sorry again, but 2litres is a little too much to gulp in one go before bed. It poses 2 risks of death. 1. vomiting/choking in your sleep. 2.Becoming hypervolemic and dying from complications, more common that you would think.