I always sit down while playing/practicing. I suspect it's something very common. Having said that, I do from time to time make it a point to stand and practice. Only because I know that if I ever am in a band and playing a live gig, chances are I will need to be standing.
As far as looking at the fretboard? Well... Unless you are special and having eye's on your fingertips, I would have to imagine that it's VERY common for beginners to stare. In fact, I stare so hard that often times it leaves my eye sight out of wack. I'll practice for an hour or two, then go to bed and try to watch TV. I can't read any text on TV for a while. It eventually goes away, but... Ok, I will also admit that I most likely need to go in for an eye checkup.
But, having said that, I do also try to make some point at playing without looking when I've become familiar with something I'm doing. However, I've watch video's were even the stars are looking at their frets.
[U]Ricks Current Mystery Video[/U] - Updated Monday March/02/2015