My DS did that for ages around that age. We used to stick him in front of a DVD and go back to bed lol. He just sat there watching happily and at some point he would go back to sleep. It would go in bursts where he would do it often for a month or two, then nothing for a few months and then it would happen again. Eventually it just happened less often and for less of a period when it did until he grew out of it.