We all understand that exercise is good for health and helps us in keeping the body fit and strong. What we fail to understand is that sometimes exercises can cause harm leading to a dangerous situation. Whenever you feel pain during the exercises, it is a sign that you must stop. Exercise can cause muscle failure and dizziness, which are serious health problems. During the workout, the blood sugar levels can fall and you can have hypoglycemia with dangerous symptoms. There can be fainting, nausea and excessive fatigue. Running can lead to severe pain while some gym exercises cause heartburn. The 5 most terrifying side effects of exercise are as follows.