I posed this over in the OUAT subreddit but I wanted to post it here as well.
As we’re all aware Snow White appeared to recognize the nightmare Aurora was describing. Snow appeared visibly upset and scared by it. This suggests she encountered the same room in her nightmares after she awoke from her own sleeping curse. Now the big question: why the heck is Henry of all people having this nightmare?
Think back to the end of season 1. Henry eats the poisonous apple, the same one in fact that poisoned Snow, turnover that Regina had made and meant for Emma to eat. Therefore we have 2 of 3 people who have suffered the exact same nightmare being linked by experiencing a sleeping curse from Regina.
By this logic we can gather that Aurora’s sleeping curse was most likely cast by Regina and maybe the red room is some sort of magical limbo your consciousness goes to when you’re under a sleeping curse. It could vary by who casts the curse and this just so happens to be Regina’s version of the room. If not, it might be a general side-effect from suffering a sleeping curse but since we only have a few cases to explore we can’t say for sure.
However this does not explain why Henry seemingly saw Aurora in her nightmare and Aurora saw Henry in hers. I like the idea of it becoming a way for Charming and Snow to communicate between worlds. That is pretty clever and would be very cool.