My brain was working overtime last night.

I woke up in a cold sweat at about four o'clock in the morning having just emerged from what I can only describe as a sort of sci-fi zombie horror nightmare, beautifully crafted by my subconscious, drawing inspiration from one of the movies it knows I can't stand, then adding in some very nice topical touches.

It took as the basis for the story the film, "28 Days Later". Now I've only seen tiny portions of this film, which found its way onto terrestrial telly quite recently, and I flicked back and forth, trying not to watch too much because frankly, those films scare me rigid. I can't do horror. This is the basic premise of the film as lifted from the internet, in case you've not seen it:

"Set in early 21st century England, the story depicts the breakdown of society following the accidental release of a highly contagious virus known as "Rage" (which renders people mindlessly violent) and focuses upon the struggle of four survivors to cope with the ruination of the life they once knew."

So there I find myself, at the top of an all but derelict tower block-cum-multistorey car park, in some nondescript English city. We're on the tenth floor. I know (not sure how I know, but I know) that floors seven downwards are full of Rage-infected zombies. In the back left corner of the room there is an elevator that will take me down, should I wish (I really don't wish). To the right, you can walk outside onto what used to be a roof garden, but what is now quite eerily overgrown and silent.

I say "we" because I'm not alone by any means. This top floor is abuzz with activity, concentrated around three or four banks of computers that vaguely resemble an old school computer room, except the PCs all look fairly futuristic. It's apparent that this is the home of some form of anti-zombie resistance movement, with quite technologically-minded Bright Young Things clattering away at keyboards, wearing headsets and generally acting like the Rebel Alliance. Outside, all is spookily quiet. Inside, it's a blur of activity.

And who's leading this last hope of humanity? My old school friend Gaby, who added me to Facebook some time yesterday afternoon. My subconscious has played a blinder in immediately casting her as the Admiral Ackbar of my worst nightmare.

The zombies never made an appearance during the dream, but I'm not sure that was any help. Instead my internal Hitchcock racked up the tension with horrific noises-off, the air rended with screams from the floors below - particularly when I briefly gazed down the ramp of the car park section of the building, toward the dreaded seventh floor. Picking my way cautiously through the roof garden it became clear that this was some kind of post-apocalyptic attempt at food production by the top floor survivors, who would obviously have to be self sustaining unless they fancied running the gauntlet of the zombies below.

At one point I was mad enough to board the elevator with Gaby. Its inspiration was definitely the lifts at Reading station, dull yellow lights illuminating the panel of numbers, an awful metallic claustrophobia setting in as the doors rattled shut. Gaby was going down to the eighth floor but I, panicking at the thought accidentally going just one floor further down, slammed my hand on the "nine" button as we reached it, then waited for the elevator back up - minus Gaby. (Plot hole: why can't the zombies board the elevator up?)

Then, an interesting turn in events. I hadn't been terribly sure what I was doing in the building from the off, but the first act had been taken up in exploring and trying to comprehend the situation. The second act, back up on the tenth floor, was for me to produce my new mobile phone - another nicely topical reference. Suddenly, I'd remembered that I worked for the BBC and was only here as a sort-of observer, albeit an incredibly reluctant one, and I very much felt my work here was done, thanks very much.

So I started tapping away at the phone, trying to enter my BBC passcode to access... well I don't know, but it felt like I was trying to access something that would get me away to the safety of a BBC newsroom as fast as possible (no zombies there, apparently - first time for everything).

Then, in the third and final beautiful element of topicality, I finished the passcode, hit "OK" and pulled this kind of transparent cloak over myself, grimacing and steeling myself for the sensation of compressed air inside my lungs.

And where did that come from? The final Harry Potter book, which finished itself (as an audio book, read by Stephen Fry) in my car last night. Harry owns an invisible cloak and can disapparate - which, as one Potter fan site will tell you, means:

"A magical form of teleportation, by which a witch or wizard can disappear from one location and reappear in another. The act is accompanied by a very unpleasant squeezing sensation, as though being sent through a tight rubber tube."

The squeezing sensation stopped, and I woke up. Genius. The only similar exit from a dream I've ever had was about ten years ago, when I somehow managed to dream a big black door with one of those luminous green "Emergency Exit" signs above it, walked through it, and awoke. But I don't think that can rival disapparating out of a zombie-infested tower block, back to the land of the living. If only I hadn't left my car on the seventh floor...