Intracranial HYPOtension.

Still a big possibility. One of the nueros I've seen said he would think more of a low pressure headache than a raised pressure headache. I was not able to see him again, he lives far from my town. He was looking for brain sag on my MRI and Intracranial Hypotension/csf leak. It can be spontaneous. To determine the pressure inside your skull is by lumbar puncture. I had one done in 2010, and it is in itself a dangerous procedure. My level was at that time normal. My headaches are no longer postural and they are not orthostatic headaches, but my symptoms are that of this condition, and many times its hard for them to find the csf leak, IF they even end up finding it. Usually a bloodpatch is applied, but noone of my doctors suggested the procedure unless they find the leak.

Good Information - 
http://www.medscape.com/viewarticle/467001
http://archneur.ama-assn.org/cgi/content/full/60/12/1713 

Intracranial Hypotension -

General Information

• Intracranial hypotension is a condition in which there is negative pressure within the brain cavity.
• There are several possible causes:
  • Cerebrospinal fluid (CSF) leak from the spinal canal:
    • A leak following a lumbar puncture (spinal tap).
    • A defect in the dura (the covering the spinal tube).
      • Spontaneous, sometimes following exertion such as swinging a golf club.
      • A congenital weakness.
      • Following spinal surgery.
      • Following spinal trauma.
    • Following a shunt procedure for hydrocephalus.
      • Lumboperitoneal shunt.
      • Ventriculoperitoneal shunt with a low pressure valve.
• In some cases, spinal CSF leaks can lead to a descent of the cerebellar tonsils into the spinal canal, similar to a Chiari malformation.
• Large spinal dural defects can lead to herniation of the spinal cord into the defect. 

Symptoms:
 - vertigo
- postural headaches
-facial numbness and pain
- visual disturbances
-nausea
-pain when sneezing,coughing or using the bathroom.
-vomiting
-hearing loss or tinnitus
-neck pain

 on MRI can show brain sag or acquired Chiari Malformation. ( downward displacement of brain matter. )