I think about it a lot, many times a day, but less than I did for the first two or three years, when I thought about it almost all the time. Sometimes my thoughts are just about the practical stuff, like making sure to find where toilets are, and judging whether or not to go out somewhere or whether it's safer not to, but in the evenings when I'm no longer busy I start to worry about what will happen if I get worse.
I've been having to visit people in hospital a bit recently and there are the horrible smells of people having their incontinence pads changed, and that freaks me out. It leads to extremely gloomy thoughts about what could happen in my old age (not so far away unfortunately), that I could end up in a care home stinking of you-know-what and no one will want to know me!
So I would say that the constant thoughts about the illness go with the territory, but if you're lucky you might think about it less as time goes by, so long as the disease is being kept under control of course.