Hi Zoggy,
I've been playing for about three years now and for the first two I always played sitting down. About a year ago I got a chance to play a bit with a band that I know and when I tried to play standing up I could'nt play a single lick. I was totally embarrassed. All thumbs, so to speak. Now I practice playing standing up at least part of the time even though I have no intention of joining a band. Hope this helps.