water/fluid, grease, paracetamol, fresh air and sleep.. in that order.
If it's the kind of hangover that almost requires medical attention then I pity you and would recommend getting Motilium tablets from the chemist, they're an anti sickness drug that take away that upset tummy/sicky feeling. Also paracetamol for the headach (with plenty of water) and get some Milk Thistle tablets from Holland and Barrett which rejuvenates your liver.
Hope you feel better soon
