For me, both the moments you refer to are symptomatic of the identity crisis at the heart of Don Draper: he isn't who he says he is and Betty, who he's hitherto relied upon to prop up his fake life, has suddenly rejected the character he's created. He's been cut adrift.
We've seen him struggling with this in New York but when he reached LA, he quickly spotted the opportunity to ditch Pete and escape into another world. The Betty hallucination represented the different worlRAB colliding.
Sure, the heat and dehydration contributed to his blackout by the pool - but it also reflected his identity crisis: here he was with people living a surreal existence almost outside of anything he's previously experienced and it became too much for him. He couldn't quite cope with it and that's why he became Dick again at the end of the episode, when he was alone - when there was nobody there to ask awkward questions ...
I don't necessarily think he'll ditch the Don persona he's adopted (I hope not!) - but I suspect he may have a few shocks in store when he gets back to New York ...