Dear patient, I totally understand your concerns about this feeling. The following causes explain what happened : 1- Since this has happened after waking up, it is possible that this might be an orthostatic hypotension. because you were lying down, and then you were up, your blood pressure can drop and causes this feeling that you are describing, that is why it is recommended always to stay few minutes sitting before standing after waking up. 2- This might be due to hypoglycemia. Since this happened in the morning, sometimes the sugar level in your blood can be low, especially if you haven t eat well the day before, hence eating something that gives you energy is also helpful in this case. 3- This might be due to vagal hypotension : sometimes if you feel fatigue, you might have such sensation of feeling about to faint because your body reacts to the fatigue by decreasing your blood pressure and heart rate. I guess this is the first time such thing happens to you, if so there is nothing to worry about Just follow the recommendations i gave you, and if this occurs note please if you feel any palpitation, take your blood pressure and heart rate and your glucose level in blood. Best Regards