Singing Range - Changed!?

My voice doesn't seem to work like it used to...one hit on the head pretty hard by a fence being pulled down on me (thanks to a paniced horse that i love still anyways) really seems to have messed up my singing range. Every year my high school choir sings the Hallelujah Chorus and I sing the high soprano, however, this year I seem to be having issues hitting the high A...or is it a high B? Well, whatever - the point is that I can no longer sing the part that I have sang easily and happily for the last three years. That really grinds my gears...but I'm working on trying to get my normal range back. However, being a lower soprano or even an alto is always an option to me because, thankfully, I have a pretty good range.