In reply to Fiona Reid: Re sitting. When I had severe sciatica I took to lying down on my living room floor and having my pc there. If you have to sit (ie at work) then get up and move around every 20mins. Sitting down actually causes more pressure and compression on your discs than standing or walking does.
Try and keep as active as possible. let your body and pain levels dictate what you can or can't do.
Physio told me to stop climbing and gave me exercises which utterly killed me but my chiropracter said I should carry on climbing. He did say hillwalking wasn't the best idea, mainly because the downhill bits put pressure on the discs (though it seems to be uphill that's worse for facet probs or stenosis I reckon)
If your climbing then avoid bouldering like the plague and when climbing my Chiro said I should try and move as fluidly as possible. Avoid big, dynamic moves and avoid high steps and big rock overs. Especially avoid moves which have you all scrunched up.
95% of folk with sciatica will get better/manage their problem with conservative treatment.
When I had it, I had bouts of being able to climb and bouts where I couldn't even walk without hyperventilating in utter agony. I ended up with masses of scar tissue chocking my nerve root and needed to have surgery to release things.
It wasn't a 100% cure though. If nerve damage goes on for a long time then sometimes it can become permanent. I still used to get numbness in my foot from time to time and my calf muscle in the affected leg has never been the same since. It's much tighter than the other one now, suffers regular cramps.
Walking (on the flat) is supposed to be the best thing you can do for your back (whoever told you to keep sat down and do nothing should be shot!)
You could suffer on and off for anything up to a year/year and half to varying degrees or another or it could get better in weeks. Try and avoid surgery if at all possible. I don't regret having it but it does change the mechanics of your spine and I'm having problems with my upper spine now (though it probably would have happened anyway)