Stretching HAMSTRINGS the right way
Lot of people think they are stretching their hamstrings when they have their leg up on a raised platform and have the pain going down all the way down the leg. That exercise is excellent at causing you sciatica,. You'll have the back and leg pain that you didn't have before.
Most people think they are stretching their hamstrings when they have their legs up at a higher platform and are trying to touch their toes or some such thing. They do it only because the guy or gal next to them is doing the same. Stop copying. Think logically. That stretch is excellent at causing pain in the back and down the leg that you didn't have before.