Bounce back up. If you're knocked down, try to get up as quickly as possible. Easier said than done, yes. But if you stay down, you run the risk of people stepping on you or others tripping on you, which could create a pile-up. If you can't get up, roll into the fetal position with one of your sides to the ground. If you're carrying a bag, hug it in front of your chest with one arm, and use the other to protect your head. “You’re trying to protect your heart and lungs,” Wertheimer says. “If you lay flat on your back, the next person who falls may put hundreds of pounds on your chest. If someone falls on top of him or her, you’ve got even more weight on you and then you can inhale, but can’t exhale.”