I would say it depends on what you want to do, and also whether your course requires occupational health clearance.

If it does require this clearance, you will have to mention it to them, but it's only up to that department whether they declare you fit and the information regarding why is not spread around the department you study from. With regards to that, I had to get clearance to return after a year out, and I was still on medication, doing ok but not great, and they just asked if I felt ok coming back. As long as you're willing to fight your corner and they can see you aren't in a terrible place then that situation would be fine I think. But this information would be obtained from your GP if you didn't declare it to them on their forms, so you might as well just admit to it.

If it doesn't require this, which most courses don't, I wouldn't see any need to mention why you'd taken time out. You could tell them whatever you like, as long as you don't get in the situation where they want a reference from what you were doing. This would also be loads easier to do if you don't have an interview, because I don't think they'd even ask to be honest.

I hope some of this makes sense. I've rambled a bit.