I had that moment not too long ago where I took a twenty minute drive to complete a task and when I got to my destination, I could not for the life of me remember any of the trip. If asked how I got from Point A to Point B, I would have been forced to confess that I was clueless. My mind had been so occupied with other concerns that it was all a fog.
It happens a lot. I can get so wrapped up into obsessive thoughts, that I forget about the here and now.
I read once that you should take five minutes each and every day to die. Sounds weird at first, but I actually did it for a while and found it to be a very relaxing exercise. All you have to do is find a populated place, take a seat, and pretend that you do no exist. Just sit there and watch the world pass you by. It did not take me long to figure out that the universe will carry on without me and strangely, that is a good feeling to possess. I am just dust in the wind, man (credit to Kansas).
The other advantage to playing the shadow is that you tend to observe a lot more than you normally would not. Unrequited love. A child's smile. Drug deals. It's as if a curtain is suddenly removed and you get a front row seat to the circus. It sort of reminds me of the X-ray glasses that were advertised in the back of comic books.
Except you can't see through people's clothes.