You live with insomnia for long enough, you start to get a knack for it. You become familiar with what that feels like, when you kind of just know that you're either gonna, or not gonna be allowed to sleep.
You usually start to understand the situation just about right when you would normally start to become sleepy. That is, if you were a normal person and not cursed. Still, you used to be a normal person, and you used to be used to getting sleepy, so there's a feeling there that comes before 'sleep time', whether or not you recognized it. A ghost of a feeling, anyway.
The way you realize that you can't have any sleep tonight is when you first start to imagine that you might like to go to sleep. This realization may occur due to a few different reasons... maybe you've been awake since the technical beginning of the day, for a dozen or so hours. Maybe you're conditioned to go to bed at a certain time. Maybe you're just plumb wore out because you worked really hard that day. Maybe you're just plumb wore out because you ain't slept in a week.
It's probably a combination of two or more of those reasons. Whatever the reason why the idea of sleep floated across your list of imminent possibilities... the thing is, right after you've thunk the sleep possibility, you'll get another feeling, and THAT's the feeling what decides that you get to sleep. Everybody gets that feeling, but nobody ever notices it unless they've ever felt the opposite of it, or the lack of it.
It's a little bit like stepping back from yourself for a second and looking at your sleep temperature, but instead of actually looking, it's a feeling. Still, the comparison works. So you step back from yourself and you can't help but see your sleep temperature, if you've gone without sleep for a while. It's not something you'd ever notice unless there was something wrong with it, or unless you were used to something being wrong with it. Otherwise, it's just as natural as your body temperature. You never notice it.
If your sleep temperature is red, you don't get to sleep. If it's blue... blessed, blessed blue... then you're one of the few people who have ever been able to know to an absolute certainty that the future is good, and kind. If it's blue, you know you'll be able to sleep, and the feeling you get is like how you felt when you first realized that you were sure, 100% without a doubt, that there is a God. It's like, this euphoric joy, the elation of just being flat-out positive of something good, that you know is real. There's no proof for it, but you don't need proof because you can feel it. It's like... being unburdened.
That's the feeling you get when you know you're going to be able to sleep, after weeks of insomnia.
The reason why I went and wrote all of this is because my sleep temperature is red today. I saw it about thirty minutes ago. And since I ain't sleeping, the idea came to me to write about what it's like. So, that's what it's like.