I hv back pain. mri shows there is posterocentral annular bulge at l4-l5 and l5-s1 level indenting the the cal sac without compression.is this serious?

First disc bulges do: Not typically cause pain & found as a normal variant on imaging studies in people without back pain. There are many reasons for back pain with most responding to non op care including: core strengthening, flexibility, cardiovascular training, avoiding tobacco use &staying trim while getting a good night's sleep. Medication options include non steroidal anti inflammatories as well as others.

No: It is not serious in terms of concern that something catastrophic will happen. What your describing is known as degenerative disc disease and is one of the more common causes of back pain in an adult. There are many nonoperative treatments that can potentially help including physical therapy.