For the last week my 2.5ds seems to have totally forgotten how to remain asleep all night. Since he was about 9months old he's managed to sleep through without too many probs although he's always been an early waker. Bedtime routine has always been the same, bath, story etc and until last week we would just give him a kiss and cuddle, say goodnight, close the door and he'd settle himself down without any fuss. He made the transition from cot to bed about 2 months ago which I was a bit worried about but it seemed to go absolutely fine. He was quite excited about his new bed and carried on putting himself to sleep happily without even trying to get out. Occasionally he'd appear in the night at our bedside but would always go straight back to sleep in his own bed after we took him back into his room.
Last week he suddenly started reappearing at the top of the stairs after we'd put him down and for a while he thought it was a funny game 
. This is now the norm and it takes around an hour until he eventually gives up and goes to sleep. He still manages to do it on his own but only after we've gone up and put him back several times. The main problem now though is he's also waking several times during the night. We try and do the same thing - put him back in bed, no interaction etc but this often can go on for an hour or more with him reappearing every few minutes or shouting for us. Last night he woke at 12, eventually went back to sleep at 1.30 and then woke at 5.30 and refused to go back to sleep.
He still naps in the day, both at home and at nursery, usually for about 1.5 hours. I can't think of anything that has changed recently so I'm confused about why this sudden change. Has anyone else experienced similar? What did you do? How long did it last? HELP!!!!