FEAR

"Fear is a projected emotion based on what may be, not what is." Dr J S Greenstein.

Constant mental reiteration of impending doom and gloom causes us to exist in preperation for the worst, even though the worst has not necessarily occured. Our minds create a possible, perhaps even probable, but nonetheless non-existent outcome of what is occuring in the present. This habitual pattern of thought alignes with related emotions precipitating a physiological response of fight, flight or freeze syndrome.

The repetitive secretion of "unnecessary" secretion of fight, flight or freeze syndrome causes the panic chemistry to reach an unjustified high, thus, in turn, stressing out mind and body.

If the worst does actually occur, you will be so busy coping with the reality of its occurence that you wont need to stress about it occuring, because it's just occured.

So, don't worry about what if, worry about what is.