Fatal familial insomnia (FFI) is a very rare autosomal dominant inherited prion disease of the brain. It is almost always caused by a mutation to the protein PrPC, but can also develop spontaneously in patients with a non-inherited mutation variant called sporadic Fatal Insomnia (sFI). 

1. The patient suffers increasing insomnia, resulting in panic attacks, paranoia, and phobias. This stage lasts for about four months.
2. Hallucinations and panic attacks become noticeable, continuing for about five months.
3. Complete inability to sleep is followed by rapid loss of weight. This lasts for about three months.
4. Dementia, during which the patient becomes unresponsive or mute over the course of six months. This is the final progression of the disease, after which death follows.