, or often simply Chiari malformation, is a malformation of the brain. It consists of a downward displacement of the cerebellar tonsils through the foramen magnum (the opening at the base of the skull), sometimes causing non-communicating hydrocephalus
as a result of obstruction of cerebrospinal fluid
(CSF) outflow. The cerebrospinal fluid outflow is caused by phase difference in outflow and influx of blood in the vasculature of the brain. It can cause headaches, fatigue, muscle weakness
in the head and face, difficulty swallowing, dizziness, nausea, impaired coordination, and, in severe cases, paralysis.
Headache in such situation could be due to sinusitis
too, this will respond to antibiotics and analgesics. Your doctor can give a course of antibiotics and see if he gets relief.
All the best .