Calming yourself on a roller coaster is a matter of managing your breathing and your physical posture. The most effective technique is "Tactical Breathing": inhale for four seconds, hold for four, and exhale for four; this forces your nervous system to stay out of "fight or flight" mode. During the ride, try to keep your eyes open and look at the horizon; closing your eyes often increases the sensation of vertigo and disorientation, which can lead to panic. Another psychological trick is to scream or laugh out loud; this releases tension and prevents you from holding your breath, which is a common cause of lightheadedness. Physically, try to relax your grip on the lap bar; "white-knuckling" sends a signal to your brain that you are in danger. Remind yourself that modern coasters are designed with extreme structural redundancies and are statistically much safer than the car ride you took to get to the park.