Fear triggers a 'fight or flight' response that speeds up your heart rate. While this protects you when escape is crucial (such as fleeing a fire), it prevents you from thinking rationally. 'Carbon-dioxide changes in your system make you feel light-headed,' says Dr Martin Antony, author of The Anti-Anxiety Workbook (The Guilford Press). Repeatedly inhale and exhale for three seconds each - a steady rhythm will focus you.