Various factors may contribute to alcohol hangover severity. The purpose of the current investigation was to evaluate the possible impact of alcohol consumption patterns, perceived immune status, and baseline fatigue on hangover severity. A survey was completed by a convenience sample of N = 199 Dutch students who reported on their latest past month’s heavy drinking occasion, including subjective intoxication (perceived drunkenness) and next-day hangover severity, which were rated on single-item scales ranging from 0 (absent) to 10 (extreme). In addition, perceived (momentary) immune fitness was assessed, and the Checklist Individual Strength (CIS) was completed to assess baseline fatigue. The analysis revealed that instead of the amount of alcohol consumed or estimated blood alcohol concentration, it appeared that subjective intoxication (i.e., level of drunkenness) was the most important determinant of alcohol hangover severity. Especially in men, albeit modest, it was perceived that immune fitness also significantly contributed to the level of hangover severity experienced.