Jingle Bells & Merry Christmas

Have you ever wondered about the word "upsot" in Jingle Bells? A few months ago (yes, way before Christmas), I was thinking about it because that's what I do. I concluded that if the author meant upset as in angry, he would have left upset. If he meant upset as in thrown out of the sleigh, then to say "upset" simply doesn't communicate. "Upsat" has a harsh ring. The word for which he sought certainly wasn't "upsit." Finally, with perfect simplicity, he rhymed, and got "upsot."

Another Christmas word-query: Why do we only say "merry" at Christmas? In England they tend to say "Happy Christmas," anyway. "Merry" means celebration and happiness. Why does "Merry Easter" or "Merry Fourth of July" not sound right? When did we start using "merry"? The answer is to be found on Wikipedia, that wealth of web knowledge:

Though Christmas has been celebrated since the 4th century AD, the first
known usage of any Christmastime greeting, "Merry Christmas and a Happy New
Year" (thus incorporating two greetings) was in an informal letter written by an English admiral in 1699. The same phrase appeared in the first Christmas card, produced in England in 1843. The then relatively new term "Merry Christmas" figured prominently in Charles Dickens' A Christmas Carol in 1843.

Also from Wikipedia, Queen Elizabeth II in England believes that "merry" means slightly intoxicated, so she officially prefers "Happy Christmas."

To God be all glory.