Thanks for you reply Debbie. I've been trying to rock him off to sleep but while he's in my arms he's all smiles, chatting away and just looking around at everything. I can rock for a very long time with not a hint of him starting to fade.
A lot of the time I end up thinking 'oh well, he musn't have been tired afterall', so we go back to the lounge room and he's back to being tired and grizzly!