The reason for this has to do with the hypothalamic–pituitary–adrenal axis, the brain's and body's stress response system that governs our fight-or-flight response.
Razlog za to ima veze s hipotalamusom, hipofizom i nadbubrežnom žlijezdom, sustavom reakcije na stres mozga i tijela što upravlja reakcijama  za borbu ili bijeg.