Immune fitness is defined as the capacity of the body to respond to health challenges (such as infections) by activating an appropriate immune response to promote health and prevent and resolve disease, which is essential for improving quality of life. Thus, immune fitness plays an essential role in health, and reduced immune fitness may be an important signal of increased susceptibility for disease. Lifestyle factors such as increased levels of alcohol consumption have been shown to negatively impact immune fitness. The alcohol hangover is the most frequently reported negative consequence of alcohol consumption and is defined as the combination of negative mental and physical symptoms, which can be experienced after a single episode of alcohol consumption, starting when blood alcohol concentration (BAC) approaches zero. Significant correlations have been reported between hangover severity and both immune fitness and biomarkers of systemic inflammation. The concepts of immune fitness and alcohol hangover are further linked by the fact that the inflammatory response to alcohol consumption plays an important role in the pathology of the alcohol hangover. Moreover, immune fitness has been related to the susceptibility of experiencing hangovers per se. It is therefore important to investigate the interrelationship between immune fitness and the alcohol hangover, and to identify possible predictor variables of both constructs. This data descriptor article describes a study that was conducted with adults living in the UK or Ireland, evaluating possible correlates and predictors of immune fitness and the alcohol hangover. Data on mood, personality, mental resilience, pain catastrophizing, and sleep were collected from n = 1178 participants through an online survey. Herein, the survey and corresponding dataset are described. Dataset: The dataset is submitted as a Supplementary File. Dataset License: CC0.