When a patient in the emergency room announces that he is feeling "dizzy", doctors find themselves having to figure out exactly what this person means by the word "dizzy". "Dizziness" is a word with a vague meaning which can make it difficult for a physician to find out the cause of a person's symptoms. Some people for instance will say they are dizzy when they are light-headed and nauseous. Other people will say they are dizzy when they feel anxious, when they have low blood sugar, or when they experience blurry or double vision. Yet others, will say they are dizzy when they have a feeling that the world is spinning around them (i.e., vertigo).
What does this have to do with stroke? Many benign conditions can make people lightheaded, nauseous,or anxious, but out of the many conditions that can cause people to feel vertiginous, a brainstem stroke is one of the most dangerous ones. Brainstem strokes must be treated emergently, as the brainstem controls many of our most important functions, such as our ability to breathe. This is why every time an emergency room doctor hears a person say "I am dizzy", he/she must make sure this person is not actually feeling vertigo, which would suggest that his or her symptoms might be caused by a dangerous brainstem stroke.
A handful of treatments are available for brainstem strokes, but for these treatments to be effective they have to be implemented rapidly after a person first notices their symptoms.
Recommended reading: How Are Strokes Treated?