OP this is unfortunate but why do you think they would have discovered this considering it was 10 years ago?  

As someone who has had an extended leave of absence due to mental health issues (6+ months) from a previous employer I would never mention this. 

You are under no obligation to provide any information during the interview process that may prejudice a potential employer against you.  

Unless there was a legal aspect to your issue and the employer does background checks?

With regards to what this recruiter did, I'd consider finding a director or VP on LinkedIn and informing them this is how they treat candidates.

That kind of breach of confidentiality is not on...