Stress can be caused by environmental stresses or ENDOGENOUS stresses as in hypoglycemia. If you want to understand anxiety attacks (unrelated to any environmental stimulus, (IOW the person does not know why?), then we are dealing with a cause of a physiological nature as in "excess adrenaline production due to a disease".
Thus in some cases adrenaline is produced when faced with an environmental stress (normal) and sometimes due to a silent disease, over which the person has no direct control.