Interesting thing about nerve pain, is that what is really happening is an inflammatory process - similar to a sprained ankle. So in acute sciatic nerve conditions, the nerve is really inflammed - so common things to do is rest, find positions that the sciatic nerve does not get aggravted, and then determine why the nerve is inflammed such as a herniated disc, pirformis syndrome, or other reasons.
Once it becomes more chronic, many people complain of a tightness in the back of the back, hip or leg along with associated nerve symptoms. From there - like an old ankle sprain - after 21 days of acute inflammation - things tend to scar and thicken. So what is happening is that the nerve is still inflammed but it is also less elastic than it used to be. Like a tight bungy cord, the sciatic nerve is now restricted in its motion, and movements such as bending forwards or doing a straight leg hamstring stretch can aggrave the sciatic nerve.
I tell many patients - the need to stretch the feeling of a tight hamstring - may well be a tightened / less elastic underlying sciatic nerve. Many times we see patients flare up trying to do so.
Please consult with a Physical Therapist that understands a technique called 'Neurodynamics' that assesses the physiology and mechanics of the nervous system to determine your ability to exercise and prevent future sciatic nerve problems.