Broadly speaking sciatica is:
Where there are symptoms in the leg, they are usually on one side only.
Sciatica can be caused by a torn disc in the lower spine or by compression of the sciatic nerve in the lumbar spine and pelvis. In most cases of sciatica the sciatic nerve is put under pressure or actually damaged.
If you've got painful sciatica, Deborah Caplan, a physical therapist and Alexander Technique teacher, recommends lying on your back with large pillows under your knees several times a day. This is a good maintenance routine as it decompresses the lower spine and helps you to stop clenching your buttocks (clenching may contribute to the sciatica symptoms.) Deborah also recommends thinking of the buttocks releasing as each leg swings forward to take a step.