In th UK its illegal now for an employer to ask this question. They can ask if any special requirements are needed for interview, or if you consider yourself to have a disability. I would never disclose, unless it was an obvious disability. I once told an employer 3 months into a new job, i might have problems sitting in on tomorrows meeting, as i have panic attacks in certain situations. Without hesitation he asked, "did you put that on your application form". I said no because it doesnt affect my work. Imagine if i said anything of other mental heath problems, i would be out the door.