The vast majority of a normal hangover would be a combination of what you feel when you haven't slept properly, because it interferes with sleep, and dehydration because alcohol is a diuretic, and encourages your body to get rid of liquid. If you've ever been in a situation where you've stayed up all night, then you already know what a lot of it feels like.
You can feel a bit dissociated, and cognitively slow. Often sore all over your body.
The dehydration can cause headaches, unpleasant GI effects, dry eyes, dry mouth, thirst.
And hangovers affect different people differently. Young people sometimes barely experience them. As you hit your thirties and up, they become substantially worse. In some people, hangovers create an unbearable kind of anxiety, which is withdrawal, and those people are very likely to end up alcoholics, because drinking relieves that hangover anxiety. So they might start having a drink int he morning so they can get through work, etc etc.