The title is key in this poem. It sets our expectations for the whole thing, letting us know that this poem is going to describe, or at least relate to, a place called Dream-Land. What's more, Poe, never uses the word "dream" again in this poem. In fact, he never talks about dreams at all. So, if you didn't have that title, you might not think about dreams at all. The landscape and the events in the poem might seem weird, but you might not connect them with Dream-Land.
At the same time, Poe definitely puts his own spin on the idea. The word "Dream-Land" sounds kind of cozy and pleasant doesn't it? Just slipping off to Dream-Land… Well, because it's Poe, things aren't quite so warm and fuzzy. The speaker seems to like it OK, but this Dream-Land is definitely not a place where we'd like to visit for very long.