You mean when you sleep walked, got a knife, and stabbed yourself, and the wet blood, because you had a nightmare
Well, taking your question seriously, there are multiple ways to answer this:
"What does a wet dream feel like WHILE YOU ARE DREAMING?" This is difficult to answer because it not only varies from person to person, but sometimes from dream to dream. And it depends on the dream you are having. Sometimes you don't remember having a dream at all! But if you do, whether it is sexual or not, at some point you realize that you "feel good" which is hard to describe, but is euphoria. You just feel good all over, no worries, and are really happy and have these tingling sensations. Your heartbeat usually increases, as if you are excited, and you might feel yourself get an erection. There will also be a feeling of "tension" that is kind of like having to pee really badly, and this is followed by the orgasm/ejaculation, which can feel just like when you are awake, or either be sped up in a quick BOOM! or slowed down to seem like a long time. It is also common, especially for boys who never had an orgasm before, to feel like they are actually peeing, but accompanied by a sort of relief that they never felt before, so it feels so good that they don't seem to care if they might be wetting the bed, but of course they could not stop the flow even if they wanted to because it is automatic. They might notice the flow occasionally stop and then start again several times.
"What does it feel like (physically) to wake up to a wet dream?" Once you wake up, you will have the memory of the dream fresh in your mind, and then freak out that you actually just wet the bed, and so nervously but quickly reach down to feel your underwear. Instead of being soaked with pee, there will be a sticky wet spot averaging the size of a quarter to a CD, and because semen is thicker than pee, will usually not soak onto your pajamas or sheets unless you were laying on your stomach. If you had no memory of the dream, you may wake up and become aware of feeling a cold wet patch on you, and briefly wonder if you wet the bed. Some don't even wake up then and only find the evidence once it has dried into a hard, crust on the underwear.
"What does it feel like (emotionally) to wake up from a wet dream?" This depends on how mature you are, how informed you are, and how independent, and the circumstances. A wet dream in front of your friends while camping or a sleepover will be more embarrassing since they may find out and tease you. Usually the first time it is scary if you have no idea what happened, you might think something is wrong with you physically or that you sinned (if religious). But usually there is some level of embarrassment or shame involved and the boy will quickly try to hide the evidence or clean it up so his mother or others won't discover the mess and what happened. If he does his own laundry or has a better relationship with parents, then it might not be a big deal. For some, you may silently cheer at the victory of such an awesome dream and having a rite of passage to manhood!
Wet, sticky, wet, warm and wet everywhere. (and all women do is complain about their periods of little dribbles!)