There are lots of weird disorders....unfortunately I don't know the names for many of them.
There is a disorder where you feel parts of your body don't belong to you, people will self amuputate.
There are brain injuries that cause short term memory loss, which means new things can't be processed into memories.
Aphasia caused by strokes.
Austism or austism spectrum disorders, but looking at a particular aspect of the disorder, for example hearing or appearant hearing disablilities associated with autism.
The one that got the book title "the man who mistook his wife for a hat" in which the brain recognition software misfired.
Dibilitating phobias.
Or, depending on your assignment, find a fictional or historical person and diagnose a disorder....Van Gogh/Meniure's Disease, Ophelia/bipolar, Bartleby the Scrivner/depressive.
I notice my spelling stinks today....I'm too tired and lazy to fix it. Please forgive me.