In terms of regular job interviews, the law is a bit complicated in terms of what questions, when and why an employer is allowed to ask re. health and disability. I certainly wouldn't voluntarily bring up schizophrenia unless it seemed to be necessary and the employer didn't seem to be breaking the law (because good luck proving you were asked inappropriate questions at interview just before you were rejected).
With med school, however, you would definitely need to contact occupational health before taking up a place. They would help you work out what you need to do/whether you can take up the place at all. I don't think you would need to bring it up in the actual med school interview (though any form of lying would look very bad if you were found out) - it's occupational health that needs the information to make the decisions on whether you can take up the place, not the interviewers who are the ones making the decision whether to offer you said place.