I'm with you all the way on the last part. More times than not I feel something like this, with the empty brain and the distraction. In a similar conversation recently, a friend of mine commented that this became a normal situation for him several years ago, oddly enough, while he was still in Canada selling real estate. He claims it's what happens when work really sets in.

Personally, I find it's just that if I sit alone for too long and don't communicate with people, my brain goes all raw hamburger like this too. I find that most of my best thinking happens when in conversation with someone else. It's become an especially pronounced problem since coming to Japan, having fewer opportunities to stretch my brain in the same analytical fashion as I am accustomed.