It's worth distinguishing between signs and symptoms, here: in short, signs are observed by the physician, whereas symptoms are experienced and reported by the patient. In tests comparing a night of heavy alcohol consumption with an equivalent amount of placebo, the only validated symptoms included "thirst, head pain, stomach distress, and feeling tired or dizzy." By comparison, no objective signs were validated (i.e. heart racing or facial flushing).
Dr. Rohsenow also notes that, although it might feel like it, a hangover isn't technically a form of withdrawal, "since withdrawal requires a different pattern of drinking (many consecutive days)."