Your question prompted me to reflect on some transition/learning years with brain fog. This is what I learned from listening to others and my own observations. Thank you for asking!

Brain fog in AS should have a 1 - 10 scale.
0 - 3 Slows your thinking a little, but, take the time to get the immediate task completed.
3 - 5 Be careful when handling sharp tools like kitchen knives or siccors. I bought safety gloves. And, double check ability to drive safely, may need to wait a day or call Uber.
6 - 8 NO DRIVING or operating vehicles. Observations, thinking and reactions become noticeable slower to others. Quick answers to questions can be challenging at times. Invite someone to reflect on your concerns to help make needed decisions as they arise during these tough days.
9 - 10 Fatigue and severe pain is often strongly associated with this level that makes simple self-care tasks hard to do. Some people describe it like just curling up into a ball (if you could) and resting. This is needed couch time with periodic stretching and light walking. Just remember sugars and carbs feed inflammation, so avoid eating unhealthy foods. Usually, I don't feel like eating anyway at this level. And, don't bother trying to make any decisions, unless there's no choice. And, except the consequences of your actions/inactions, just do what you can when you can to correct any mistakes or omissions. This took years for me to learn.

Omg yes, I forgot what a cup was once, thank goodness I have family members that take care of me now. They can help with my memory stuff, getting around at times and remembering meds. I feel for all going thru this, it royally sucks. I try to explain myself to people all the time. I'm flighty....I talk about one thing n move on to different things all the time or forget what I was talking about all together ugh.

Im forgetting a lot, ill get on my computer to look up something, then wind up doing something else, completely forgetting what I was supposed to look up.

Yes I do I didn't realize it was from Spondylitis till I read this..

On the plus side tv reruns are always new! Lol. I have some dementor in my family as well. Some fought it and became nasty and miserable. Others just kept smiling and went for the ride. I’m determined to just try to enjoy the ride. Don’t worry que sera sera , what ever will be will be, it’s all good unless you allow it to be not. Good luck!