Strokes can happen without warning and typically result from a blood clot in the brain. People experiencing a stroke may suddenly be unable to walk or talk. They may also seem confused and have weakness on one side of their body. As an onlooker, this can be a frightening experience. If you don’t know much about strokes, you may not know how to respond.

Because a stroke can be life-threatening and lead to permanent disability, it’s important to act fast. If you suspect that a loved one is having a stroke, here’s what you should and shouldn’t do during this critical time.

Do call an ambulance. If a loved one is experiencing a stroke, your first instinct might be to drive them to the hospital. But in this situation, it’s best to call 911. An ambulance can get to your location and get the person to a hospital quicker. Plus, paramedics are equipped to handle different types of emergency situations. They can offer life-saving assistance on the way to the hospital, which can potentially reduce the damaging effects of the stroke.

Do use the word “stroke.” When you call 911 and request help, notify the operator that you suspect the person is having a stroke. Paramedics will be better prepared to help them, and the hospital can prepare for their arrival.

Do keep track of symptoms. Your loved one may be unable to communicate at the hospital, so the more information you can provide, the better. Keep a mental or written note of symptoms, including when these symptoms began. Did they start in the last hour, or did you notice symptoms three hours ago? If the person has known medical conditions, be prepared to share that information with the hospital staff. These conditions might include high blood pressure, heart disease, sleep apnea, or diabetes.

Do talk to the person experiencing a stroke. As you wait for the ambulance to arrive, gather as much information from the person as possible while they’re still able to communicate. Ask about any medications they’re taking, health conditions they have, and known allergies. Write this information down so you can share it with the doctor, in case your loved one is unable to communicate later on.

Do encourage the person to lie down. If the person is sitting or standing up, encourage them to lie down on their side with their head elevated. This position promotes blood flow to the brain. However, do not move the person if they’ve fallen. To keep them comfortable, loosen restrictive clothing.

Do perform CPR, if needed. Some people may become unconscious during a stroke. If this happens, check your loved one to see if they’re still breathing. If you cannot find a pulse, start performing CPR. If you don’t know how to perform CPR, the 911 operator can walk you through the process until help arrives.

Do stay calm. As hard as it might be, try to stay calm throughout this process. It’s easier to communicate with the 911 operator when you’re in a calm state of mind.

Don’t allow the person to drive to the hospital. Stroke symptoms can be subtle in the beginning. The person may realize something is wrong, but not suspect a stroke. If you believe the person is having a stroke, don’t let them drive to the hospital. Call 911 and wait for help to arrive.

Don’t give them any medication. Although aspirin is a blood thinner, don’t give someone aspirin while they’re having a stroke. A blood clot is only one cause of a stroke. A stroke can also be caused by a burst blood vessel in the brain. Since you don’t know which type of stroke the person is having, don’t give any medication that could make bleeding worse.

Don’t give the person anything to eat or drink. Avoid giving food or water to someone having a stroke. A stroke can cause muscle weakness throughout the body and, in some cases, paralysis. If the person has difficulty swallowing, they could choke on food or water.

A stroke can be a life-threatening situation, so don’t delay in seeking help. The worst thing you can do is wait to see if symptoms improve. The longer your loved one goes without help, the more likely it is that they will be left with a permanent disability. However, if they get to the hospital soon after experiencing symptoms and receiving appropriate treatment, they have a much better chance at a smooth recovery.