At my Fed. Gov. job, I changed from not having a disability to Code 84 Diabetes after I had been at my job a long time and was in the job I wanted… I struggle with that decision. But there are times because of diabetes I can find myself not following rules, or doing things that a supervisor would see as interfering with work. Such as sitting at the desk with a low hoping no one calls for 10 minutes, or pulling off the road in a gov. vehicle for a candy bar when you are only suppose to stop for fuel or a meal. That code 84, may help explain some of my actions, even though I would probably have the same rights without declaring it.
Here is a link to Q and A on diabetes as a disability.