You don't get hangovers from painkillers, if you are addicted you can have withdrawals. (which I don't think you are since you have only been taking them for two days)
You will be fine, just don't take more than the recommended dosage.
vicodin is a strong painkiller which can make you feel sleepy, lethargic and sometimes nauseated. You probably wont have a hangover as such but perhaps you could take half the dose at night instead?