If you suspect someone might be having a stroke, remember the mnemonic F-A-S-T for rapid assessment:
F - Face. Does one side droop down? Can they smile?
A - Arms. Ask the victim to raise his/her arms. Are they unable to or does one arm seem weak and paralyzed?
S - Speech. Can they move their lips or mouth? Do they slur the words? Can they even understand you?
T - Time. Get to the nearest hospital quickly. Strokes are considered a life-or-death emergency.