It can cause you to become sick, because stress releases a hormone and too much of this hormone weakens your immune system, which lets diseases take over easier. Also you get headaches and moody and what not. Hope this helps :)
Stress can cause you to become sick. Some of the symptoms that you are sick because of being affected by stressing are like headaches, lack of sleep or bad sleeping patterns, anxiety, feelings of frustrations and flu's and colds that you get more frequently. See more details at http://stress.about.com/od/understandingstress/a/stress_symptoms.htm.