Which effect takes precedence?
I doubt there's an official rule to cover this. The possibilities I can think of, with my favorite bolded:


You aren't delayed at all - you just return. Seems too...nice for Arkham, like you're cheating your way out of the bad effects of an encounter.
You are delayed, so you stay in the Dreamlands one more turn then return to your original location. I think this makes the most sense in terms of the ideas of the cards - you fall asleep, end up in the Dreamlands, and you wake back up as soon as you're done with whatever you find yourself doing there. In this case you find yourself stuck there, so you have to wait until you stop being stuck there to be done and wake back up. 
You are delayed and also return immediately, so you're stuck in your original location for an extra turn. If you squint at the rules, this seems totally logical: "stay here next turn" = "delayed" = "skip your next movement". It just feels a little weird flavor-wise.
You are delayed so you miss out on your chance to return to Arkham so you're stuck in the Dreamlands. If you really want to go by the spirit of "the worst possible thing always happens to you in Arkham", this is your option, but turning a mostly-benign Arkham encounter into a waste of several turns (delayed, stand up, move, try to return and get lost in time and space...) seems pretty excessive.