Am I accountable for anything if I have a wet dream, given that I could have prevented it because I woke up before it happened?

A wet dream during the daytime in Ramadan does not affect the validity of the fast because it is something beyond one's control. A ghusl (ritual bath) is required if semen is discharged. However, if no semen is discharged, then nothing is incumbent upon the person. If a person intentionally causes semen to be discharged (masturbation), this is forbidden and invalidates the fast. One must then make up that day and repent to Allah.