i have 31,000 in medical bills due to personel injury claim what is a decent settlement offer

Your question cannot be answered based upon the information provided. Various factors such as permanent residual medical impairment and future treatment issues need to be considered.  Likewise, the type of concussion is relevant, and sciatica can be a symptom of a chronic back sprain all the way up to a ruptured disc. Given all of the potential variables, I cannot provide a resonable settlement value or range.