Stroke happens when blood flow to part of the brain is interrupted, and acting fast greatly improves outcomes. The FAST checklist is the easiest way to remember the key signs: Face drooping on one side, Arm weakness when raising both arms, Speech that is slurred or hard to understand, and Time to call emergency services immediately if any of these appear.
Other sudden warning signs include numbness or weakness of the face, arm, or leg (especially on one side), sudden confusion, trouble seeing in one or both eyes, sudden severe headache with no known cause, and trouble walking, dizziness, or loss of balance and coordination.
Do not wait to see if symptoms pass, even if they seem to improve. A brief episode can be a transient ischemic attack (mini-stroke) that warns of a larger stroke to come. Note the time symptoms started, because that information affects which treatments can be given, and call your local emergency number rather than driving.