The only way to know that you are getting the correct amount of oxygen is to check the oxygen level in your blood while using oxygen therapy. Too much oxygen can be as dangerous as not receiving enough, and for that reason, you should follow your doctors directions precisely. If you do develop new symptoms, such as increased sleepiness, confusion, headaches, etc., you might be getting too much oxygen, and you should notify your physician immediately. Do not change the liter flow or hours of usage without first checking with your doctor.