Most poems about dreams side with the dream. Donne's speaker is woken from a happy one and, after a moment's reluctance, is grateful. The woman who woke him did not break the dream but "continued'st it", and she is so real that thoughts of her "make dreams truths, and fables histories." Waking has given him something better than sleep, so he invites her into his arms to "act the rest" of what the dream left unfinished.
The second movement raises the compliment higher. She woke him with her eyes, "as lightning or a taper's light", and not with any noise. He took her for an angel at first sight, but she knew his thoughts, and even "when / Excess of joy would wake me", and that goes "beyond an angels art." The last line of the section is the cleverest: "Prophane to think thee anything but thee." The religious vocabulary is deliberate, since a confession of faith has been moved into a bedroom. The compliment is that she needs no comparison, because she is her own standard.
Then the poem turns on a three-syllable line: "Thou art not thou." Her coming and staying "showed thee thee", but her "rising", which I read as her getting up to leave, makes him doubt she is still herself. The logic is sharp and a little bitter. Love is "weak, where fear's as strong as he", and a love mixed with "Fear, Shame, Honour" is not "all spirit pure and brave." The poem never says what she fears, but the capitalised abstractions suggest worries about reputation. In the last image, she is a torch that men "light and put out" as needed. She "cam'st to kindle, go'st to come", and the phrase packs her leaving and her return into one clause. It sounds like a reproach, and it is also the speaker talking himself into hope.
The form supports this swing. The poem runs in three ten-line movements with the same rhyme scheme, abbaccddee. The line lengths also repeat: two tetrameters, a very short line, a pentameter, a tetrameter, then pentameters. That short third line is where the speaker's thought snaps shut or snaps around. In the first movement it is "It was a theme", where the dream is weighed against reason. In the second it is "Yet I thought thee", the angelic mistake. In the third it is the paradox about her identity. The closing couplets work like a lock clicking into place, and the "thee" rhymes ("me/thee", "be/thee") make her the poem's fixed point. Even the archaic verb endings, "waked'st", "brok'st", "continued'st", carry the intimacy of "thou", and "continued'st" stretches the line to match what it describes.
Donne also writes in the language of argument: "Therefore", "yet", "for since", "But", "Perchance". These words make the poem sound like a man reasoning with himself in real time. The ending shows why. The last couplet runs over the line break ("Then I / Will dream that hope again, but else would die"), so that the "I" is left hanging until the rhyme word "die" lands on it. The speaker has come full circle: the dream he was glad to leave is now the place he must return to, because it is the only place she reliably stays.
That reversal is what makes the poem worth reading. It begins as a flattering love poem, then turns into a fear of losing the person who has just proved she was better than fantasy. Its wit is playful, but the closing note is not. The speaker has learned that the real thing can outshine the dream and still leave him with nothing to hold, and he admits that hope is all he has.