Many marathoners, even the experienced ones, don't sleep well the night before the marathon. You may be nervous, excited, or both. But don't worry. Get a good night's sleep for a night or two before that last night, and you'll be just as well off than if you slept soundly the night before (not that there's anything wrong with that). On marathon day you'll have adrenaline to make up for lost sleep. And you will probably sleep soundly for the next few nights after the marathon.