NoHorse is right. I'm also a Utah horse owner and alfalfa is everywhere- I got lucky when my grass hay dealer was nearby. I don't know much about alfalfa, but I heard from a close friend of mine that it can cause flounder and muscular issues... But, on the plus side, I believe that it had nutritional benefits. So I feed both alfalfa and grass, try to get the best of both worlds. My horse is four, so he'll have some hyperactivity just from age and personality alone, but as long as he's not out of control I don't change a thing.
As for hyperactivity, also, I have rarely seen a horse where alfalfa effects their energy in a negative way. I say rarely because I actually never have- but I'm sure some exist out there.
Step one: Mount horse. Step two: Stay mounted.