It is simple: it disturbs the flow of energy in your system.
Stress means pressure!
It is an external or internal force impacting on your energy body.
If you release that tension, the energy flows again.
Now, if you stay stressed for many months or years, the energy blockages crystallize nodes in your energy system and these disturbances remain until they are cleared.
These disturbances are the possible cause for residual emotional tensions and sicknesses as well.
The key to stay in good health is to make sure that your energy system is harmonized.
To your life force!