Mental disorders are diagnosed by a licensed professional, a number of different tests are used and graded accordingly. Depending on the scores the appropriate diagnosis is made.

Alzheimer's disease

Eric Clapton was not diagnosed with any mental disorders. His drummer Jim Gordon, however, was diagnosed with Schizophrenic.

Einstein wasn't diagnosed with any mental or physical disorders.

Sleep disorders are listed in the DSM( the Diagnostic and Statistical Manual of Mental Disorder). They are considered axis 1 disorders. They can be the basis of sole diagnosis, but are most often diagnosed in concurrence with another disorder.