Here's a more personal interpretation:. I think this song is, as many have said, about the hard times ("dog days") being over, but I think the bits where she says "she hid under beds" and "run fast for..." and especially "you can't carry it with you if you want to survive," all kind of indicate, for me, a sense that the happiness was resisted at first, ("from it she fled") Obviously it came on very suddenly (with all the images of horses and bullets and trains), but have you ever been in a situation where happiness is beckoning to you, but because of everything in your past, and bad experiences and memories, and fear of the situation going south, you resist going forward into it? I definitely have, and that's why I love this song so much. Florence nailed it. I think she has fallen in love very quickly, and is afraid to get too far into it because of her past negative experiences, but, "you can't carry [those] with you if you want to survive." In fact, she's sort of accepted it already, as she says "from someone who should have known better" and "can you hear the horses? Because here they come." This song is like the moment the dawn breaks.