Sleepwalking - has it happened to you?

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Tonight while watching cricket on tv, my grandson fell asleep. He had been sleeping for about 30min when he started sleepwalking and talking in his sleep, saying he needs a door, over and over. I have no idea what he was dreaming. I have also walked in my sleep a few times, but my husband has always woken me up before I get too far. Can you tell me what causes sleepwalking.