How To Cure Sciatica?

I have symptoms of sciatica. I have had it before and was out of action completely for 3 weeks. will going to the gym aggitate or relieve symptoms? (walking/jogging on treadmill; crosstrainer) I am scared it will get as bad as last time. The last attack was in Nov 2010, a scan showed some disc problem but nothing major. I understand it was muscular. I am 45, generally fit and healthy, but do have lower back problems at times. Exercise keeps this at bay.