It's due to a prolapsed disc. You will not make the D2D ride if you have sciatica! It is caused by a bulging disc pushing on the sciatic nerve. Rest and do not over stretch!
A year ago I went through similar, it does get better, almost a full feeling of recovery but it takes time. If you go back to early it'll last longer. Slow rides when you feel up to it, not when things are acute!
I'm not sure if everyone above had sciatica, a session at a drop in centre would not cure a prolapsed disc – maybe you had something other than sciatica, as nickhart say's, it is horrendous! I couldn't even put a pair of socks on in the morning, the pain was so intense, and it would just set it off again for the day. Kneeling at the table to eat, because I couldn't sit etc etc.
Getting back to the point, it does slowly recover, six weeks is the time you should see some improvement however small. Then you will be on the road to recovery, just don't do anything silly in the meantime!