Heh
Yes TM875, stress has a chemical, i.e. objective basis in reality. If it really had none and we believed it, we wouldn't eat, sleep, or act on any of our basic needs.
It has some subjectivity in terms of the way different individuals may interpret and deal with situations, but in respect of physics and biology it is real (for instance, I work on a busy bar and can deal with it, but at first it did seem very stressful after working in a quiet shop. I got used to it, but a busy night can still make my muscles ache and make me feel a bit frazzled).
Short bursts of mental or physical stress are good exercise, as long as they don't overwhelm your capacities. Long periods are wearying and unhealthy.