Hugs, could defiantly all be teeth. The canines and molars made Z super grumpy and fussy...
Can you resettle at the 5am WU? - if not try sneaking in at 4am and stirring him (not waking) and then sneaking out to see if it will reset his sleep cycle. If it works I'd do it for 3 nights.
Alternatively you could push the nap out a touch later, if it's been at 12 a long time. But with the EW that will be hard...