Like fear of being blind or fear of having a mental disorder is that fear enough to actually make the brain mimic symptoms of it?
These are pretty common and can cause considerable distress to people. Common forms include health-anxiety ("I'm having a heart attack"; "I have cancer"). Less common forms include blindness or paralysis.
A complicating factor is that people reject the treatment because they feel they are being ignored or dismissed as "making it up" or "faking it".
It can be tricky for clinicians to work with someone with a somatic symptom disorder. How do you respond to someone who claims to be blind, but who does stuff that requires sight?
https://en.wikipedia.org/wiki/Somatic_symptom_disorder
> A somatic symptom disorder, formerly known as a somatoform disorder,[1][2][3] is a mental disorder characterized by physical symptoms that suggest physical illness or injury – symptoms that cannot be explained fully by a general medical condition or by the direct effect of a substance, and are not attributable to another mental disorder (e.g., panic disorder).
https://en.wikipedia.org/wiki/Conversion_disorder
> A conversion disorder causes patients to suffer from neurological symptoms, such as numbness, blindness, paralysis, or fits without a definable organic cause. It is thought that symptoms arise in response to stressful situations affecting a patient's mental health. Conversion disorder is considered a psychiatric disorder in the Diagnostic and Statistical Manual of Mental Disorders fifth edition (DSM-5).[1]
From Wikipedia: "Voodoo death, a term coined by Walter Cannon in 1942 also known as psychogenic death or psychosomatic death, is the phenomenon of sudden death as brought about by a strong emotional shock, such as fear."