Learning a language uses a lot of mental energy, and since I have been working really hard at my Spanish here (with great success I might add), I've been wearing out my poor little brain. It can get to the point where I can't form coherent sentences in my own language.
I have noticed that stress, and not enough sleep make brain drain set in faster. So I really have to manage my time effectively.
I'm getting better at resting my brain drain gauge, and have come up with two great tricks that work as mental fatigue reset buttons.
1. Coffee naps!
I'm lucky to be learning a language in a country that has siestas. When I hit that two o'clock slump, where my brain can do nothing more than make train noises, I drink a shot of espresso, lie down, and take a 15 minute power nap. The caffeine wakes me up, and my brain is fresh and ready for another round of abuse.
A walk works really well, but I think it's better to break a sweat. My favorite way to reset my mental gauge is to cranks some really girly music (Miss A, Katy Perry, 4minute, Ke$ha...) and dance like a drunken monkey. After about 15 minutes, my brain resets and I'm capable of forming coherent thoughts again.
I find that more exercise I get, the longer I can work my brain before brain drain sets in.