Everyone gets sick. We all occasionally miss work. However, if you are going to miss work more than 2, or maybe 3, days of work on average due to your medical conditions, there are very few employers who are going to keep you as an employee. If you have chronic medical condition that is causing you to miss work frequently, then you could be considered disabled for that reason. However, you must have a doctor support you in saying that you would most probably have that limitation. Also, your doctor should have some reason to believe that is the case.