So I'm going to go ahead and, as you might imagine, respectfully disagree with this wonderful youtube comment on the video for Salem's remix of Britney Spears' Till The World Ends.
The basic point of singing "We'll keep dancing till the world ends," seems, fairly obviously, to me at least, to be not a point about the apocalypse, but about dancing. And specifically, about what one avoids doing by dancing. Which is to say, fucking. To take the song as being about the apocalypse, then (which, admittedly, the video does, albeit a very mild apocalypse, one which is obviously situated in the contemporary mythological vernacular ("DECEMBER 21ST, 2012") and which cannot only be avoided by dancing in a sewer for a couple minutes, but can be actively watched approaching from a few blocks away with no ill effects), seems fairly inane.
The video is, on the other hand, pretty blatant about its citation of Spears' I'm a Slave 4 U, which it recontextualizes into an apocalyptic setting. In this light, the fact that dancing is basically an elision of fucking in Till The World Ends becomes more pertinent, as I'm a Slave 4 U was very much a song, both in itself and in the context of Spears' career as a public figure, a song about (dancing as) fucking.
Which isn't, of course, to say that I'm a Slave 4 U doesn't defer sex, but on the contrary that how it does so is basically identical to the deferrals of the visual/aural grammar that has colonized sexual entertainment - in a word, pornography. It adheres to the syntax of submission and fragmentation, the visual dismembering and aesthetic re-membering of bodies as signifying vehicles with the phallus as master signifier. Till The World Ends is, on the other hand, about holistic bodies with mastery over themselves, reacting in the face of crisis.
Because dancing is, essentially, a question of the body's mastery of itself, in which the mind is elided. This is where, incidentally, Black Swan either succeeds miraculously or fails miserably, depending on whether you view it as a melodrama, a genre concerned with hysteria and the general question of the mind's intrusive presence in the face of its obsolescence, or as any other genre. Viewed as melodrama, the narrative arc of the film is not about Portman's character losing her mind due to stress or mommy issues, but is rather a film about a mind that is radically disconnected from its body (of necessity) restructuring, according to its own (symbolic) grammar, the events of the body's learning process.
It's worth noting, as well, that Spears is not exactly the most technically accomplished dancer among her peer group. Her dancing, while frequent, is always jagged, a product of consideration rather than impulse, primarily consisting of controlled arm movements while stepping to the beat. Her dancing is, it might be said, more arithmetical than primal, an expression of the mind (whether mechanically, as premeditated actions being carried out, or creatively, as symbolic gestures) which employs the body as its tool. There is actually an argument to be made, I think, that I'm a Slave 4 U is the point at which Spears transitioned into a project in which her primary goal began to be to naturalize this form of dancing which directs attention away from (or, perhaps more accurately, past) the explicit, which is to say the body, and towards what is implied. And what is implied by dancing, quite naturally, is usually fucking.
This, then, is the real sense in which Till The World Ends is an apocalyptic song. It is an unveiling, as the culture that sustained Spears' project is in the process of being displaced by a culture which, heralded by dubstep and textualized by Gaga, has no room for it.
The video for Hold It Against Me then reveals itself to be a particularly canny mixture of autopsy and apocalypse, as Gaga's visual aesthetic is linked with the projection of old Spears videos through a dubstep-influenced aural environment. And the symbols of the video become an unveiling as well, as the implicit argument throughout her older videos that Spears' bodily perfection is, paradoxically, the reason she is not an accomplished dancer becomes basically explicit as her monstrous progeny spring forth from her giant wedding dress and dance quite well, or her obvious body doubles battle each other for domination.