Nerves of Jello

Tomorrow is the Mora Half Marathon. It will be the third time I have run the race, but for some reason I am feeling nervous. This is absurd. The distance is manageable (I've run further each of the past two weekends), I don't have a particular pace that I need to keep (although I would like to finish in under two hours), and no one else I know will be there (so I don't need to "keep up appearances" for anyone). I do not understand. If I am feeling this size of butterflies now, what will it be like as October 7th approaches? Tomorrow or the next day I can report on the Mora Half, but for now I need to find some Tums.