Human: What are the main causes of a hangover? Assistant: 
The main causes of a hangover include dehydration, alcohol consumption, and fatigue. Dehydration can occur when you have not replaced your fluids during or after drinking, which can cause headaches, dizziness, nausea, and vomiting. Alcohol consumption can also lead to an increase in blood sugar levels, which can result in a headache. Fatigue is caused by the body's inability to process alcohol quickly, which results in a feeling of tiredness and discomfort.