Go to a cafe or restaurant or some other nice place and get some coffee or tea to calm down. Alternatively if you aren‘t living alone, stay with your friends. Being alone can give you nightmares or be terrifying after such experiences (unless you prefer that now). If your fear gets worse, you can also go to a hospital and let them give you some meds. You‘re under shock now and should definitely not be alone atm, so any nice place with people around is best.