It's a particular kind of alone-ness, and for me it's productive. Fuelled by tea and exhaustion, but with a weird kind of clarity about it. And then when you eventually reach the required word count you fall gratefully into an unmade bed and let the exhaustion overwhelm the kind of insomnia which comes from worrying that you still have far too much to do and too little time to do it in.
I remember the first time I pulled a true all-nighter, which was also the day I started smoking. I was still awake at maybe 4am, not having started my college work which I was meant to be handing in the next day. I noticed a classmate was still online and messaged him asking how it was going. Somehow we ended up chatting and then arranging to catch the first morning bus and meet at a coffee shop in town. "Okay," I said, "It's a deal, but you have to crash me a couple of fags." He was silently amused, and we agreed, both a little shocked in the end that the other actually turned up. We lasted until lunchtime on around three coffees and caffeine pills and then we simultaneously felt terrible. I've since learnt that the caffeine actually makes this a lot worse, but still, that crash time is awful.
Other awesome reasons for staying up at night - being really, really addicted to a TV show so that you just can't stop watching it, one episode after another, until finally falling into weird surreal dreams which are half about this universe and half about something completely different. Or a game, that works too. Getting way too involved with some argument on the internet. Sex, obviously, the kind in a new relationship where the lack of sleep literally seems to have no effect on your daily life at all. Getting drunk with your best friends, smoking too much and laughing until your lungs hurt, or having the kind of conversation which gets to the very heart of your soul. And being awake with a newborn baby, when they're tiny and it feels like there's just the two of you there in the world and this amazing little person looks at you and you realise that to them, there are only the two of you, because you are their entire world.
I hate being sleep-deprived, and the hell which is the next day (especially with a toddler) means that I don't do this very often, but staying up until god-knows-when is good for the soul, or at least it is for mine. It has to be done, and if I can plan ahead and allow myself a slob day, or an early night, or at least someone to muddle through with, then it's definitely worth it. Hell, it's worth it even without a chance to catch up.