I think they'll tell a lot from the way you are, if you chat willingly, are positive, your body language etc...
If you went in and did yourself down and were difficult to get talking, did yourself down and seemed very downhearted about things, had defensive body language, they may think you're not quite in the right place yet, especially if the job is in a team.
Maybe they will want to see how you talk about what happened, do you find it hard to talk about and get defensive or are you open and relaxed and positive about things to show you're moved on.
Depending on the job, maybe they want to check your emotional state eg how you'd deal with authority or problems, would you be strong about things or emotional or find it hard to cope.
Another factor is whether you would be able to work normal hours without a lot of time off sick say if you felt you couldn't face work or cope with something, imortant that the stressful thing has been removed from your life and you're not still in a harmful environment.
Important for future colleagues or other people you'd come into contact with as to how you interact with people, how certain situations may affect you, eg paranoia or withdrawing. It is also important for the nature of the business.
Hope that gives more of a general idea of the things they may be looking for and good luck :) x