Reasons of your most terrible nightmares

Dark-dark night. You go on the empty street and suddenly hear steps behind the back. Having turned back, see the terrible clown with an axe which every second everything is closer. As though you were not accelerated, it does not lag behind. Ominous laughter, and suddenly feel a hand on the shoulder. Breath stood, a rumble in ears … You wake up. For certain something similar happened at everyone. In dreams we quite often meet the main fears face to face. But why it occurs? Found out together with the doctor-somnologom, professor, MD Roman Buzunov. It appears, that we got used to call nightmares, not always...