I Looked it up for you. Here are the relavent points based on the information.
Vicodin is a hydrocodone barbituate. Basically, it is 2-8 times as potent as codine, so it is a very potent pain killer.
A warning tagged to bydrocodone is that it produces dose dependant respiratory depression by acting on the brainstem respiratory centre, so your respiration will be decreased.
Sedation, drowsiness, mental clouding, lethargy, impairment of mental and physical performance, anxiety, fear, dysphoria, dizziness, psychic dependence, mood changes and blurred vision are all side effects of the drug on the central nervous system.
Dry mouth is also another side effect that may help to explain your dehydrated feeling.