I have spoken to our ped about this because DD was having very bad night terrors (different from night mares). She told me that sleep walking, sleep talking, night terrors are all hereditary. Chances are someone in your family sleep walks. DD does all 3 (not the night terrors any more though.) She also said that it tends to go in cycles. Will happen often for a while, then disappear for possible months on end, then return without warning. Nothing to be worried about, as long as she is safe.