I have a herniated l4 l5, and i get occasional sciatica flare ups. i feel tightness in the muscles at the bottom of my back, which is relieved by stretches. why does this happen?

Neural Compression : Disc herniation means that the disc gel has moved from a sequestered space between the vertebra and into the spinal canal. here it will crowd and compress either the spinal cord and/or nerves that flow out from the cord through the neuroformamin (holes to allow nerve passage) . Causing your symptoms. Often the gel resolves after a few weeks, and benefits from epidural steroid injections.