I would just try to get in a good long sleep a day or two before the 18th, then just do what I had to do on the 18th/19th. I'm not a napper, myself, but if you're able to do it, it wouldn't hurt. As far as the run goes, if you're tired, just grab some caffeine on the way, get some breakfast about 2 hours before your run, and have a good time. You'll just be up maybe an hour or two past your normal bedtime, and the energy of the crowd and the running will carry you through.