I was in a bit of a slump between about 1998 and 2005 or so. You wouldn't really know it from looking at my cv, though. I continued to write and publish. There are no gaps, periods of more than 2 years without significant publications. From my perspective I was in a slump, because I was writing more than I was publishing and having a hard time putting together a book manuscript. I wasn't having a very good time in my job and suffered from mild to moderate depression. What I did, essentially, is write myself out of it. Now it is clear to me that the work I did during this period wasn't wasted in the least, but I went 15 years without publishing a book.
I still bear some ill effects from that period. It took me longer than it should have to become a full professor, and my salary is still far below where it should be in relation to my accomplishments and those of comparable people in my department. I was barely hanging on in terms of living a satisfactory life, but I was still able to write, somehow.
Now I'm in a phase where I'm asking myself "what next?" I need to make a change of some kind for purely financial reasons. This means either getting another job where the renumeration is decent, staying at Kansas as Distinguished Professor, or taking on some kind of administrative job. None of these is a sure thing in a stagnant economy, but I need to try to make some move at this point. If I retired tomorrow I would have had a kick-ass career in terms of pure scholarship, but there are many things I have left to do, and the most urgent of these things is to make a little more money so I can eventually retire in comfort.