Vibration / buzzing sensation in pelvic area when bending neck / head forward. is this lhermitte's sign? compressed nerve? cervical herniation?

Lhermitte's sign: is also called barber's chair sign. The electrical sensation can be quite alarming indeed. A more common cause of this in a 41 year old lady would be a demyelinating disorder like MS or Clinically Isolated Syndrome. Other localizing signs and symptoms will help with deciding how to proceed in the work (MRI of a portion of the spinal cord, brain or both). Other cord issues need to be excluded.