I have a habit of arching my back forward while I put it on the wall.. It was an obstacle but, rather then focus on getting it correct, I thought it would be easier and more comfortable if I left it there. And it was, mostly due to the fact that I'm pretty skiny for my height, and my spine can easily be felt/the "bumps" can be seen. So having a hard surface on them was rather uncomfortable..
After I stopped focussing on my back, I found it pretty easy to clear my mind a few minutes afterwards. Easier then the void meditation on a candle flame, in y opinion; however, I have not done that in some time. But I keep getting the "tunnel vision" I suppose, only everything goes blurry and fades out, including my focal point. So I would have to refocus my eyes often. I tried taking slow, deep breaths, but didn't want to focus on my breathing to much also..
Unfortunately, like with every meditating session, I did the zen meditation sessions at night, right before bed, which made falling asleep rather difficult. XD But it's the ont time when it's somewhat quiet in my house so I won't complain. =P
Next time, should I pay more attention to my back posture and my breathing?