I believe that you go into repayment 6 months after graduation unless you have already cut into your deferral time, in which case they could become due sooner. So, technically you could go into repayment during gap year. If you can't afford it, you can request a forbearance, but interest will continue to accrue. Once you're in medical school, you can have an academic deferral again. In deferral, your unsubsidized loans will accrue interest but your subsidized will not. At least, that's what they told me.