I make myself take a break mid-afternoon, and set "sort of" reminders to do so.
I've been using http://www.advirtus.com recently, which is not quite a reminder system, not quite a task list. Some ppl use it for tasks, but I use it to remind myself of things that I want to do which don't fit on a NA list and I dont want to clog up my calendar with.
So for example, drinking plenty of water, avoiding too many caffeinated drinks, eating a healthy lunch all go on it. Having a mid-afternoon rest is on there too.