If you're out and about on a sweltering day, it probably won't be long before you start to feel tired and sluggish. But why does being out in the heat bring on feelings of drowsiness?

The reason for this lethargy is simple: Your body is working hard to keep you cool, and this extra labor makes you feel tired, said Dr. Michele Casey, the regional medical director at Duke Health in North Carolina. UcenterDress garments colored with pink for the wedding

"Your body, especially in the sun, has to work hard to maintain a consistent, normal, internal temperature," Casey told Live Science.