Exposure to sunlight and heat results in natural reactions in the body that may deplete some of your energy, making you feel sleepy. However, fatigue can also be a sign of a more serious condition, such as dehydration or heat exhaustion.
Exposure to sunlight results in a number of chemical processes in the body, including absorption of vitamin D, vitamin D3 sulfate and cholesterol sulfate. In addition, exposure to heat results in the body's cooling system kicking in, which causes sweating. These natural processes cause the body to work harder, even at rest, which may result in a feeling of sleepiness.
Dehydration and heat exhaustion are heat-related conditions caused by a depletion of water and/or salt intake. These can possibly result in heat stroke. One of the first symptoms of dehydration and heat exhaustion is sleepiness or fatigue. Other symptoms include headaches, muscle cramps, pale skin, profuse sweating and rapid heartbeat. Anyone suffering from dehydration or heat exhaustion should drink water, remove tight or hot clothing and take a cool shower immediately. If symptoms remain or worsen, call a doctor.
To prevent dehydration, always drink plenty of water and wear loose, cool clothing on hot days. Take extra caution when working or exercising outdoors, making sure to consume water two hours before working or exercising outdoors. Also, remember to consume water or sports drinks right before and during work or exercise.