Syncope. Most probably a sudden drop in blood pressure. Your blood pressure needs to be checked sitting and standing to see if there is a drop. One simple maneuver you can try is to stand up with your head down then gradually bring your head up.
Fainting. When you feel like you are going to pass out after a sudden change in position, you could be experiencing a rapid drop in your blood pressure. This can be due to dehydration, anemia, medication problems, heart problems, or other issues. You should be seen by a physician to have this evaluated and get some blood tests run.
Low Blood sugar. There may be several factor but first have you doctor check you morning blood sugar.
Blood flow. Benign condition such as transient orthostatic hypotension refers to a drop in blood pressure that occurs with the position change of either lying/sitting to standing. Standing causes the blood in the body to move downward due to gravity and pool in the legs. This results in decrease blood to the brain and a sense of fainting. Medications can also cause similar symptoms. Please see your doctor.