This is because anything directly exposed to the sun will absorb its radiated heat, irrespective of the air temperature. To cool down, avoid ground that's been exposed to the sun for a long time or dig underneath the surface. In the high Andes you can broil in the sun and shiver in the shade, inches away from each other. A breeze normally cools you down because it evaporates your sweat more quickly. If the wind is strong enough, however, it can turn a basic scorcher into a blast furnace, dramatically accelerating moisture loss.
Clothing can help to reduce the effects of wind.
As your body functions, so it generates heat as a by-product. The more work you make your body do, the more heat it puts forth. It's worse if the outside temperature is not what you are used to. Your body needs time to acclimatize if it is not used to being in hot environments. All rights reserved.