I've been doing some reading lately about how the human brain works when it comes to emotions, and one of the most important things I've found out so far is just how damaging (unnoticed) stress can be.
I'm not a biologist or a neurologist of course and all I know is what I read and what I know from some basic medical studies, so if anyone here knows more about this than I do feel free to correct or complete anything I say that may not be accurate, but here's a very simple version of how stress works:
Either you experience a short jolt of fear or anxiety and your adrenal glands pump a dose of (nor)adrenalin into your system to up your heart rate and provide the muscles with extra blood so you can instantly "fight or flee". However in our society what's more often the case is that a problem is not solved by fighting or fleeing, and that it persists for days or weeks (stress at work, financial situation, relationship problems, etc.) and so another, way more subtle, long-term stress reaction needs to take place.
Simply put your brain sets in motion a hormonal chain reaction resulting in the release of cortisol by the adrenal glands. The levels of cortisol that circulate in your body go up a hundredfold when this happens, yet it's very likely that you will not notice this. Unlikely (nor)adrenalin cortisol only has effect over time and among other things simply makes sure your muscles get enough sugar and that your immune system stays suppressed (this can also be medically explained but I'm trying to keep this short) for extended periods of time. Note that this is the kind of stress you usually do not feel even though it is very present and has serious biochemical consequences for your body.
Now there is one specific part of our brains (our hippocampus) that is responsible for inhibiting the hormone that sets this stress reaction in motion, and returning the body to its previous, peaceful state. In other words the hippocampus is the reason we can deal with stress.
Here is the problem.
Prolonged levels of cortisol in your bloodstream can not only cause muscle damage, diabetes and fatal infections if severe, but in a very ironic and sadistic mechanism to stimulate the hippocampus to inhibit the stress hormones, cortisol effectively "attacks" the hippocampus and inhibits the multiplying of its cells. The result is that people who have experienced extended periods of stress often have a damaged hippocampus, and consequently no longer have the physical capacity to deal with stress efficiently.
This even goes so far that children who have had traumatic childhoods and such more often than not have a severely shrunken hippocampus and simply cannot cope with stress like other people can. On top of this science has indicated that this is one of the main causes of depression; stress reactions that are not effectively dealt with by the body. So in conclusion: living a stressful life inhibits your capacity of dealing with stress in the long run and seriously ups the chance of developing depressions.
I also don't think that people whose hippocampus is damaged or smaller due to previous trauma/stress are doomed for this, I think with enough willpower and mental practice this problem can be minimized and overcome; and in the very worst situation temporary medication would have to be taken, but this is by no means something that should control your life. The reason I'm posting this is because many people don't know the dangers of stress and neglect stress management under the assumption that once it's over it's over and there won't be permanent damage.
Moral of the story: avoid stress whenever you can, practice meditation or yoga if you have to, but don't neglect tension and stress management.