Bad night from being put down til about 30 mins after we went to bed. He was waking every 5-10 minutes at some points.
Eventually 5mls of calpol, one further wake up needing settling, then a final wake up a few mins later where the calpol knocked him out he self settled. And that was it til 7.
Thank fuck.
No idea what it was, it's not teeth.
I did think was it something he ate, but he's not had anything unusual. 
Chasing what a clever little monkey! O bashes the cups together, and looks at them, but no attempts to do anything with them, even though I have shown him 16 gazillion times! 