Sciatica is generally caused by sciatic nerve compression.
Disorders are known to cause sciatic nerve pain include:
Lumbar spine misalignments
herniated or bulging discs (slipped discs)
pregnancy and childbirth
Tumors and non-spinal disorders such as diabetes, constipation, or sitting on one's back pocket wallet.
Sciatic nerve compression may result in the loss of feeling (sensory loss), paralysis of a single limb or group of muscles (monoplegia), and insomnia.