Maybe the most important thing you should know about stroke is that it is always an emergency. Always.

A stroke can occur when a blood vessel that feeds oxygen and blood to the brain is blocked by a clot. That's called an ischemic stroke, and it's the most common kind. According to the American Stroke Association (ASA), ischemic strokes make up about 87 percent of strokes.

A stroke also can occur when a blood vessel ruptures, spilling blood into the surrounding brain. This is called a hemorrhagic stroke. Hemorrhagic strokes account for about 13 percent of all strokes, according to the ASA.

A stroke starves the brain of the nutrients it needs. If a stroke interrupts blood flow to a particular part of the brain that controls a body function, that part of the body won't work normally.

That's why stroke is a leading cause of disability in the U.S. It kills brain cells. Quick medical treatment is crucial to minimize the long-term effects of stroke and to reduce the risk of death.

The major symptoms of a stroke can be best remembered by the acronym FAST, which stands for:

Face drooping. Does one side of the face droop or is it numb? A quick way to assess this is to ask the person to smile. Is the smile uneven or lopsided?

Arm weakness. Is one arm weak or numb? Ask the person to raise both arms. Does one arm dip downward?

Speech difficulty. Ask the person to repeat a simple sentence. Is their speech slurred, or are they not able to speak at all?

Time to call 911. This isn't a symptom, but instead an urgent reminder to get help right away—even if the symptoms go away. The best way to get emergency medical help for a stroke is to call 911.