Firstly, let's define Stress.
Stress is defined simply as 'Change'.
Any kind of change. Be it nvironmental, Physical, Emotional or Social - Good or Bad. As human beings we are naturally resistant to any type of change. So prospect of anything in our well-defined lives changing, puts our bodies on 'Full Alert'.
Between ages of birth and 6 years old, we lay down our jigsaw puzzle of life. Our subconscious minds carve out a plan of what is acceptable, believable, achievable and realistic. From learning that putting your hand on red circle on stove is sore, to associating a raised voice with a deed deemed to be unacceptable.
This is subconscious laying out set of rules that determines survival. If you want to not only survive, but function well in world, these are rules you have to live by.
Good girls don't do that..., boys don't cry..., don't mix with them they're not our class etc etc.
Thus starts process of Stress. The subconscious will hold onto its 'Survival Jigsaw' against tremendous opposition. The moment it perceives change, defenses go up.
It is a proven fact that some of us handle Stress better than others. About 10% of population actually has a lowered capability of adjusting to change, and seeing it as a welcome challenge. The chemical imbalance in their brain causes them to be acutely aware of, and sensitive to, change. The results are Depression, Insomnia, Irritability, PMS amongst others.
We all know that power of our thoughts, has ability to influence our physiology. 'As you think, so shall you be'.