Well, the mystery is solved. I didn't remember buying the yearbook because Microbio Daughter bought it as a gift for me a year or two ago, knowing how much I wanted one. She found it while packing for her move and left it for me to see!
I wasn't going crazy or falling into dementia. No one was trying to gaslight me, though I think "Gaslight" is a great movie. I have been forgetting minor things lately, but that's one of my migraine symptoms. But I didn't forget about having a yearbook that I wished for in order to reminisce about some of my high school years and as I come in contact with more high school friends online. I can relax and enjoy the book!
On a similar note, I found a couple of videos from when I was in marching band. The quality of the videos aren't the best, but you can see how awesome our band was. We spent our summers practicing and marching, and you can see the results of hard work.