Yeah, just keep a monolog going in your head. So and so was the raiser PF, he bet out the flop, ect. If you find yourself getting lost then its time to step away and go do something else...your mind isn't in it.

For me, the biggest indicator of not being focused is loses. If after a hand I lost I can analyze it and call it a bad beat or a tough break then I am fine. If I was behind all along, I examine if I really am up to poker right now. After several lost hands that you can't call a bad beat it becomes quit clear I just am not up to it right now... and I logout.