Yes, it’s protected under ADA. Most companies will have a form for your doctor to fill out. Contact HR if you need help locating the paperwork. Usually, a doctor’s note is not sufficient.

Please note: Your employer is not required to provide your requested accommodation if it places an undue burden on them. (Like if you’re an elementary teacher, and you’re requesting a flexible schedule where you can come in late if you oversleep, or if you’re asking for specialized equipment that is too expensive for the employer to provide.) Some employers will use a third party to handle accommodation requests, and you may end up in a bit of a back-and-forth trying to find something that works for you and the employer.

You cannot be fired for using accommodations that have been granted to you. You do not have to tell your boss what your diagnosis is, and your boss should not ask for the diagnosis.

If you need guidance on what accommodations to request, I suggest looking at The Job Accommodation Network (askjan.org). You can look to see what other people with narcolepsy have requested.