Why are you so tired the next day after being in the sun all day?

Being in the sun all day can lead to fatigue due to a combination of factors. Prolonged sun exposure can cause dehydration, as the body loses fluids through sweat to regulate temperature. Additionally, the heat can strain your body, making it work harder to cool down, which can be exhausting. Finally, the overall energy expenditure and potential lack of sleep due to a disrupted routine may contribute to feeling tired the next day.