Much of this diagnosis comes from the clinical history. Specifically, a positional component. Meaning, the headache goes away or improves significantly when lying down, and worsens after standing up, typically within 15 minutes. It occurs most often from a spontaneous spinal fluid (CSF) leak in the spine. However, if there is a lot of clear drainage from the nose, CSF leaks can also occur into the sinuses and nasal passages. ENT (ear nose and throat) doctors have a test that they can do to test the fluid from the nose to see if it is CSF or normal sinus/nasal drainage. Please refer to one of the prior responses regarding other testing.