"Hydrocephalus is an abnormal accumulation of cerebrospinal fluid (CSF) within cavities in the brain called ventricles. Cerebrospinal fluid is produced in the ventricles and in the choroid plexus. It circulates through the ventricular system in the brain and is absorbed into the bloodstream. This fluid is in constant circulation and has many functions, including to surround the brain and spinal cord and act as a protective cushion against injury. It contains nutrients and proteins necessary for the nourishment and normal function of the brain, and carries waste products away from surrounding tissues."
So basically, when this fluid can't be absorbed properly it produces this condition. So far the only "treatment" is via a shunt apparatus, which is basically a pump attached to a tube by which the liquid can travel from the head to any area of the body to be absorbed. (The most common areas for absorption are the stomach or the heart.)
For more information, please visit http://www.hydroassoc.org/
On good days, you feel no headaches, and can go about your day.
On not so good days, you're constantly dealing with headaches.
And on bad days you have to haul it to the hospital to get checked out, and possibly even deal with surgery. And yes, I mean brain surgery.
As you can imagine, an operation like this has it's effects. In my case, I suffer from loss of focus and short term memory problems, which means I have to write EVERYTHING down. I kid you not.
If you ever meet someone with Hydro, ask them about it. I'm sure they'll be happy to share their story.