Here is some information from the Mayo Clinic on Heat Stroke:

Heatstroke is a condition caused by the body overheating. This usually happens because of exposure to high temperatures or physical activity in high temperatures for too long. There are a few stages of heat injury, and heatstroke is the most serious. It can happen if body temperature rises to 104 F (40 C) or higher. Heatstroke is most common in the summer months.

Heatstroke needs emergency care. If it's not treated, heatstroke can quickly damage the brain, heart, kidneys and muscles. This damage gets worse the longer treatment is delayed, which increases the risk of serious complications or death.

Symptoms

Heatstroke symptoms include:

• High body temperature. A core body temperature of 104 degrees Fahrenheit (40 degrees Celsius) or higher is the main sign of heatstroke.
• Change in mental state or behavior. Confusion, agitation, slurred speech, irritability, delirium, seizures and coma can all result from heatstroke.
• Change in sweating pattern. In heatstroke brought on by hot weather, skin feels hot and dry to the touch. However, in heatstroke brought on by strenuous exercise, sweating may be profuse.
• Nausea and vomiting. Someone with heatstroke may feel sick to their stomach or vomit.
• Flushed skin. Skin may turn red as body temperature increases.
• Rapid breathing. Breathing may become rapid and shallow.
• Racing heart rate. Pulse may significantly increase because heat stress places an extreme burden on the heart to help cool the body.
• Headache. Heatstroke may cause the head to throb.

When to see a doctor

If you think a person may be experiencing heatstroke, seek immediate medical help. Call 911 or your local emergency services number.

Take immediate action to cool the person with heatstroke while waiting for emergency treatment.

• Get the person into shade or indoors.
• Remove excess clothing.
• Cool the person with whatever means available — put in a cool tub of water or a cool shower, spray with a garden hose, sponge with cool water, fan while misting with cool water, or place ice packs or cold, wet towels on the person's head, neck, armpits and groin.

https://www.mayoclinic.org/diseases-conditions/heat-stroke/symptoms-causes/syc-20353581