@JPB,
JPB, No, I don't think the time of year has anything to do with how I'm feeling. Extreme isolation is more likely the cause. I haven't seen anyone other than doormen, cab drivers, doctors, and store cashiers since November. Total isolation.
I'm also worrying about money. That always contributes to the problem.
Sorry to hear you're depressed as well. Phooey to that.
In my neck of the woods and in my business, the comma in question is called a series comma. Every book publisher I've ever worked for has required the series comma. On the other hand, many newspapers and magazines, don't use them. Why? Ask 'em. I got other stuff to worry about.
Every publisher that I know of has its own house style that all the writers, editors, and proofreaders must follow.
IMO, the series comma is a good clarifier.