Thank you all so much for your input! Yes, it IS an Easter Cactus - you got me on that one! As soon as I posted I knew I was wrong! When I bought it this spring, I thought it was just a Christmas cactus gone crazy blooming that time of year, but I wasn’t about to tell it that! I attempted the running alcohol on a q-tip solution when I initially noticed the problem (maybe a week ago?). It was hard to get the dot off - it looked like an orange/brown dot with a clear layer of slime over the top (probably a bad description!), and didn’t immediately come off, but eventually did once I “helped” it a bit more with some harder pressure. The plant is outdoors and is in the shade most of the time. If it gets any sun it’s afternoon sun. I water once a week, but I have a moisture meter and check the moisture first. Right now it’s reading as very moist/wet, which, I know, is not a good thing. It was potted in a mix of cactus/succulent soil, sand, and pearlite, so it should be draining well. I’m in California where it’s been 100°+ for a while, so the fact that it is not drying out is a little worrisome. Hopefully I watered it recently and forgot! The pebbles on the top were a deterrent to gnats that I read about, and I also like the look. However, if it’s causing the problem, it’s back to sand for me! yes, Rina, I would love some pics. I took one as close as I could (my phone camera doesn’t like to focus close up when I want it to!) of what I scraped off with a q-tip and alcohol today. Maybe it will help! I’d like to save the plant if at all possible. It’s not huge or terribly sentimental, that’s true, but I’d like to keep it if at all possible, just the same. Thanks again everyone for all of your help!!!

I do not grow opuntia, so maybe I shouldn't comment. Here is my question: IIRC, corking starts at the base of the plant. I can't tell from he photo if it does or not. Corking is normal for many (maybe all???) cacti. It is usually relatively slow process. But if brown spots apear in other spots on plant, and suddenly, rather than at the base, it is a problem - caused by pests disease or damage.

It appears, from the photo, to have a fungus infection. I'm not sure what to do about it.

HU-866... your plant looks nice & green, and leaves are plump. In 1st photo, I THINK I see some dark segments - not the corking! - but not sure. Also, bottom of the pot is quite stained, & that suggests to me prolonged periods of time standing in too much moisture. I could be wrong, but if correct, the roots could be damaged. That could signal begining of root rot & may cause the leaf loss...Plant will likely take some time to recover after repotting, so be prepared. I think pot is large, & wouldn't use bigger. Could be wider (or the same size), but if, than shallower. And remember: these are epithypic plants that need very good drainage.