Taking Extended Unpaid Leave

I am planning on returning to my current bank for FT, but I'm not sure if I will be able to stick it out for two years. I could feel my health deteriorating a bit over a 10 week internship, so I can only imagine what two years of real responsibility will do to me. Is it unheard of for analysts to take 1-2 months of unpaid leave and still return to their job? Is it possible to do this within the first year, or is it something that only second years could do? I don't care much about my bonus. I just want to make it through two years in one piece.