Bottom Line: Sciatica is leg pain, numbness, or tingling, that originates in your low back. And wow can it hurt! The sciatic nerve is the largest nerve in your body. It is made up of individual branches (or nerve roots) in your lower back that combine to form the sciatic nerve which then travels down into your leg. Sharp pain which can increase when sitting, and weakness in your leg/foot making it difficult to walk are a few common symptoms that pop up when the sciatic nerve is pinched or irritated.