DS waking on some sort of High????

[Charlee]

DS is 22 months he's been a fairly good sleeper for ages he sleeps on his cot matress on the floor as he can easily climb out of his cot and prefers his 'big boy bed'

The last week or so however he has taken to waking at 10pm on some sort of high it seems, jumping around, screaming shouting as if it were morning time, there is not an ounce of sleep in him but he wont stay alone so im up untill the wee hours of the morning watching him while he plays as if it were day time.

He goes to bed at 7pm usually with no problems. He used to sleep through until 7am.

Any ideas anyone?