Imagine your perfect summer day. Maybe you’re on a long hike with friends or working in your garden with your spouse. Maybe you’re playing catch with your kids in the back yard or on a jog through your favorite park. You start to feel a little ill—clammy, nauseous, a slight headache. Then, all of the sudden, your friends notice that you’re confused and disoriented.

These symptoms are all signs of heat illness growing more serious. Confusion is a sign of heatstroke—the most severe form of heat-induced illness. Heatstroke is very dangerous and can develop very quickly. That’s why it’s so important to be able to recognize the signs—and take action quickly—if you or someone with you becomes overcome with heat.

Here are four essential things to know about heatstroke.

1. Heatstroke is a True Medical Emergency

Heatstroke occurs when the body can no longer get rid of the heat it absorbs. The key symptom to watch for is an altered mental state—confusion or odd behavior. A person may have seizures or go into a coma. This is an emergency situation, and every minute counts. The person should get immediate medical attention. Even if they start to feel better, they still need to see a doctor.

2. Anyone Can Get Heatstroke

There’s a misconception that relatively young, relatively healthy people aren’t at risk for heatstroke, and that heatstroke can’t happen unless it’s extremely hot. The reality is, anyone’s body temperature can reach dangerous levels with the right mix of heat and strenuous activity. In fact, people who are not used to extreme heat may be less likely to recognize the signs of heat illness or not use air conditioning or other cooling methods.

At the same time, parents and loved ones should pay particular attention to heat illnesses and heatstroke in older individuals as well as children. Keep close tabs on them as temperatures go up and watch for symptoms.

3. Cooling is the #1 Treatment

If someone is disoriented and suffering from heatstroke, the first step should be to call 911. Then, do everything you can to cool that person off. A few key actions to take:

• Get them out of the hot environment—move them into air conditioning or shade
• Get them cool—take off clothes or excess layers, use fans
• Get them wet—simulate sweating using cool towels or misting
• Get them hydrated—give them cool water or other fluids to drink

Medications designed to reduce temperatures from a fever should not be used to address heat illnesses.

4. Heatstroke Can be Prevented

Heatstroke is scary, but it can be prevented. If you know you’re going to be in the heat or working up a sweat, a few precautions can go a long way in protecting yourself. Wear loose-fitting, light clothing that protects you from the sun without making you too hot. Drink a lot of fluids to start the day with a “full tank.” Here’s a good rule of thumb around hydration—if you don’t feel the urge to urinate after a few hours, you’re probably not drinking enough water.

Whenever you’re outside in the heat, make sure you have water with you, along with your cell phone (with GPS). If you’re hosting or attending an event outdoors, provide water and fans—or bring extras for others.  If you cannot avoid being in the heat, try to take frequent breaks in a shaded area or even better, an air-conditioned room.

Often, we’re inclined to push ourselves or ignore potential symptoms when we’re in certain social situations. We’ll push ourselves during a pickup basketball game or feel like we can’t step away at an outdoor wedding or party. It’s important to be aware of your surroundings and how you’re feeling. If you start to notice signs of heatstroke in yourself or others—there’s no time to waste.