It was a great night and such and such a fun but you drank too much and now not feeling particularly well. To tell your spanish speaking friends that you are hangover you should say:

-Tengo resaca (I'm hungover, used in Spain)
-Estoy cocido / Tengo la cruda (I'm hangover, used in Mexico and other Latin American countries)

Other sentences that you might use could be:
-Creo que anoche bebi demasiado
(I think I drank too much last night)
-Tengo un dolor de cabeza terrible
(I have a terrible headache)