Re-applying to the PhD Program after Illness I started in a combinded MS/PhD program and was on the PhD track, but for mental and physical health reasons I had to switch to the MS track. I had not yet made it to the research part of the program, so I don't have an adviser.

I really want to get my PhD, and the (then) graduate director in my department told me when I made the switch that I'd be able to apply to rejoin the PhD program after getting my Master's. I'm getting my Master's in the spring, so I'm working on the application now. I just don't quite know what to do with the essay.

The essay is supposed to be about my research interests, career goals, and reasons for choosing the program. I think my health issues will be sort of an elephant in the room if I don't say something about them, but I'm worried that saying too much will make me look like a weaker candidate than I am. I've had these health issues for most of my life and will continue to have them for the foreseeable future, but they're more under control now than they were a year and a half ago when I made the switch.

How much is too much to reveal about this whole situation? How much is too much of my essay to spend on it? Is there any way to spin this situation in a positive (or at least neutral) way?

(I wasn't sure how much detail to include in this question, but I'm happy to go into more detail if it would help.)
I'll slightly replicate my answer to this question: mention this, but don't be too melodramatic. You have dealt with an illness that was out of your hands and got a handle on it. This is not something that a reasonable admissions committee will see as a point against you, but be sure that they understand you are not looking to get accepted because of your illness. It is also might be illegal to discriminate against you because of illness, depending on its nature and the country you're in. 

Good luck!