When you have chronic (years) of decreased sensation in the limbs, coordination and balance problems, half of the throat paralyzed, constantly pissing oneself, cognitive issues, etc, and they can't find a reason for it then it's an illness with verifiable symptoms but has not been diagnosed.

People with spine issues, MS, Lyme, and Lupus for example usually refer to it as "limbo land". Neurological diseases are notoriously difficult to diagnose and often go without an official diagnoses for months, years, and even decades.