Huge difference: do you have that condition before you go to prison, or does it start afterwards?
If you have it before (plus all the papers certifying it), then they are going to care properly. Doctors & judges can even decide that a person is unable to go to prison (this happens often when people are very old).
If you get it later, then the procedures take awfully long, and in the meantime you will probably not get all the care that you need. Plus some really bad treatment by other inmates.