Why does staying indoors too long make you feel unwell?

When you stay indoors too long, your body may not get enough sunlight. Sunlight helps your body produce vitamin D, which is essential for keeping your immune system healthy. Without enough sunlight, you may become Vitamin D deficient, which can make you feel unwell. Additionally, spending too much time indoors can lead to an increase in air pollution and a decrease in the quality of the air you breathe. This can also make you feel unwell.