Crib made of coals?

So our formerly awesome napper has turned into a little troll. It is as if his crib has magically turned into hot coals. He can be all sleepy, yawning and rubbing his eyes. He can be ready to fall asleep on my shoulder, but the instant that little baby butt hits his crib mattress his eyes fly open and there is much squalking and complaining, and if not retrieved this escalates to crying with sad little baby curled bottom lip.

It is probably some combination of him being more excited and engaged with the world around him and therefore more interested in fighting naps, and possibly even some early stage separation anxiety (it seemed to start around my trip to ASA in San Francisco). But either way it is the pits. It hasn't yet spread to night sleep (thank God), but the last two days the only way I could get him to sleep was to wear him around for an hour and a half while he slept in the sling. I love him and was actually secretly a little glad to do it because it made me feel all needed and connected to him like when he was a tiny sprout. On the other hand, he now weighs more than 20 lbs and wearing that weight on one shoulder for an hour and a half is no joke.