Scheduling: One thing that has helped me is to develop a schedule that enables me to stick to certain habits but also gives me some mental time off. I find that I am very diligent about studying when I am at school, so when I am on campus I try to get as much done as possible. If I have flexibility in planning classes, I'll try to schedule them early so I'm on campus as soon as possible. I also have some habits that help. I workout right when I get up and that helps my day get going. And I realize my pitfalls, so I try to avoid them. I deleted facebook from my phone and hardly ever check it. I'll probably be off SDN in two weeks when school starts back up. And I give myself a break periodically. This is crucial.
And just as the poster above said, I found that shadowing and volunteering this past year really kept me on track. It reminded me why I was doing this. It helps if you find a specialty or activity that really resonates with you.
Is it worth it? Check back in August of next year when I find out if I am going to med school or not. I did well on the MCAT, so my discipline for studying on campus really helped with that. And I'm trying to be disciplined with getting my applications completed at medical schools this year. Part of what makes it worth it is knowing that you've pushed pretty hard during the week and then doing something completely random and unplanned. I like a combination of routine and spontaneity, so it's the little random unplanned activities that often make working hard worthwhile.