what does it mean when you sit down and when you get up you cant move your left leg? its like its always numb. what is this a sign of?

Could be a simple natural effect of limiting ur leg's blood circulation because of ur sitting position or posture. Could also be a complication of longstanding hypertension. Do u have diabetes? Numbness and pain of extremities manifest in diabetes patients. I recommend having ur blood pressure taken as well as Fasting blood sugar level.

sounds like your circulation is being cut off. If it continues go see a doctor.