The first semi-physical symptoms are irritability and scattered focusing ability. These behavioral symptoms are quite easy to notice on others before any actual physical symptoms appear.
The most common physical symptoms are pain (which may begin as discomfort) and tension.
If the stress is severe, but relatively short term (for example, your boyfriend/girlfriend has just broken up with you), a crushing stomach pain, erratic breathing patterns and sharp headaches may appear.
If the stress is less severe, but ongoing for a relatively longer period of time (for example, doing the same work every day), bad posture, back pain, shoulder tension, never ending dull headaches may be symptomatic of such a situation.
After a certain threshold the whole body begins to suffer damage, and this in turn invites other imbalances and illnesses - causing more numerous and more severe physical symptoms.