Can Time Slow Down?
Your perception of the passage of time is calibrated, among other things, by your peripheral vision. Peripheral vision is designed to detect movement. Natural selection most likely gave it to us to detect predators that are moving at us fast. What happens is your emotions will change your focus of your eyes which then change how quickly you detect movements. Then your calibration for time is off because how sensitive you are to detecting movements is off. Hence the saying "Time flies when you're having fun". Most likely something to do with the nervous system. When you're frightened your focus sharpens, and so does your peripheral vision, and therefore time will slow down.