That whole shaking on the ground mess is just a farce. Most of the time it's for show, but other times, the person(s) caught up in the moment, for lack of a better term, "spazzes out" because either that is what is expected of them, they have seen others do the same, or they are emotionally unstable to begin with and are easily coerced into a convulsive or "I've got JEEEEZUZ!" state. That's not to knock the feeling of peace and excitement that can come with knowing and accepting that Jesus is our personal savior and wanting to live your life according to God's will and His plan of Salvation, its just that I think 99.9% of these instances are merely theatrical performances for the benefit of those watching and have no actual bearing on the person's salvation.