If you see someone exhibiting one of these symptoms, call 911 immediately:

1. Sudden numbness or weakness of the face, arm or leg (especially on one side of the body)

2. Sudden confusion, trouble speaking or understanding speech

3. Sudden trouble seeing in one or both eyes

4. Sudden trouble walking, dizziness, loss of balance or coordination

5. Sudden severe headache with no known cause

From www.ninds.nih.gov/disorders/stroke