The answer?

News flash: we think we may have found the reason for Ari's sudden night waking....a tooth!
Feeling around Ari's bottom gum this morning, I felt something distinctly sharp - and noticed a little red mark.
Which means I probably shouldn't be feeding him should he wake in the night - I'm supposed to be dosing him up with Panadol/Bonjela and putting him back to bed. We'll see...