How do you turn off your GTD mentality when you need a break? Say you've even scheduled free time to do whatever it is that relaxes you. Perhaps what relaxes you are some of the personal projects you have going on, or playing with your pet, that sort of thing. How do you "turn your brain off" so that you can focus on.. not focusing?
I think this is a really interesting question - because I very much approach it from the other side - as in 'Because I know that I've got all the things I need to do written down in a system that I trust, I generally am quite relaxed'.
What I think might help, might be looking at the question as "How do I avoid the urge to fill every waking moment with productivity, to avoid feeling like I'm on a treadmill all day?" This is also a pretty interesting one. In my mind there are two main motivations for increasing productivity
People of type two are people who don't have to worry about switching off - people of type one start approaching a mentality where every waking moment should be advancing your career/fitness/mind (and when we move into ultraman sleep schedules, is when we start to increase the number of waking moments to be productive in.
As far as I'm concerned - group activity is the cure, take a class, go bowling with friends on, have something on your schedule that blocks off some time disconnected. Big and obvious one is, of course, spending time with the family :)
One technique you can try is just to start doing your relaxing activity, and if you start thinking about work, instead of trying to "not think" it, acknowledge it. Then you can quietly shift your focus easily and the distracting thoughts won't pop back up. (In my experience particularly strong distractions may take several attempts to shift focus, but it does happen.) I use this meditation technique sometimes when I'm trying to sleep but I have too much going on the really relax. It's like a child begging for attention. If you ignore the kid they'll just keep at you, but if you turn and say "ok, I see you, but I'm busy right now so go and play and I'll come and get you when I'm ready", they go and play and you can finish what you were doing.
Another way of thinking about it is if someone tells you "Don't think about a pink elephant"...thinking about not thinking automatically makes you think it. The thing is, having the image of a pink elephant pop into your mind isn't Game Over (or work-related issues, or bills you have to pay, etc). Acknowledge the thought, "Oh, look, a pink elephant", then move your focus elsewhere and you'll find that's the end of the elephant.
This has always been a big problem for me: I get very ansty and feel like I'm wasting time if I'm not always making progress in some way. But I've also found that even if I'm not ticking off items in my todo list, I feel fine as long as I'm doing an activity where I make progress towards some kind of goal.
That's why I tend to choose hobbies where there is some notion of progress. For example, playing a musical instrument is relaxing, but doesn't bother the GTD side of my brain because I'm improving my musical skills.
Conversely, just watching whatever is on TV is something I could almost never do—but if I'm watching a specific show that I'm interested in, I can feel like I'm making progress by getting through all the episodes of the show.
When I socialize, I try to make sure that I'm meeting interesting new people, or at least feel that I'm getting to know people—people who I care about—better.