I am on disability, finally, after getting too ill also. Even tho I loved my career, it meant the world to me, it's just not worth it making me sick from stress. Sometimes it gets to that point where you have to choose. Even stable on meds, I have to "baby" it and avoid that kind of stress, it's kind of fragile.
If you are determined to go back, good for you and Kittycat is right about the "personal" reason. It's the truth, and none of thier business. If they press, just stop the interview and leave. That's not a good sign.
I am concerned, tho, because you are already having anxiety issues. It can unstabilize you so be aware of that fact and stop at the first sign of problems before you end up in the hospital, because once you get full blown hypo/mania or depression, it's harder and harder to come back, ok? not worth it.