How will having elevated brain pressure affect my long-term health?

Bad, bad, bad. Elevated intracranial pressure causes many difficulties in addition to permanent changes to the optic nerves, loss of vision, enlargement of the ventricles of the brain, and potentially brain damage if not corrected. The brain is a very delicate structure and should be treated very delicately. Make sure you are getting proper treatment and vigilant followup.
Follow it carefully. By elevated "brain pressure", you may mean a condition called pseudotumor cerebri. This is a condition of elevated intracranial pressure, usually diagnosed by a lumbar puncture. Management includes weight loss, medications, and occasionally shunting. If managed well, you can avoid long term complications. These can include: headaches, visual loss, neurologic symptoms such as numbness.