I am very glad that I read this thread because it never would have occurred to me that making excessive trips to the lav would make fellow passengers nervous. So yesterday, while flying on 844 from JFK, I simply announced to the entire F class cabin what my intentions were each and every time I got up. I asked whether anyone objected to my use of the lav, apologized for my very frequent visits and promised that I was mostly harmless, at least as long as there was no turbulence while I was inside. Everyone seemed to appreciate this courtesy and to take my pronouncements fairly well.