During severe heat stroke, the body becomes so overheated that sweat glands and other organs don't function normally. Symptoms include weakness, dizziness, headache, nausea, and high fever which can lead to loss of consciousness. Heat stroke is a life-threatening condition. Seek immediate medical attention. Take breaks often and drink plenty of water.
Heat exhaustion is caused by the failure to adjust to extended exposure to high heat.
Symptoms include weakness, dizziness, headache, and nausea along with blurred vision and mild muscle cramps. The skin becomes damp and cold and profuse sweating may be present. Heat exhaustion is easily reversed by rest, drinking fluids and applying cold compresses to the body before the symptoms become severe. The summer sun is really hard on eyes. When choosing sunglasses, look for a label that tells how much protection the lenses provide from ultraviolet, or UV rays.