It's a mixture for me.
Sometimes, it's rather like the school Physics lesson where they show the movement of molecules as a substance is heated under pressure, where each molecule is a thought, a thing to do, the different parts of the task all like the different electrons/protons enclosed in a shell, all bouncing around and colliding with other tasks, creating heat (stress) until I have to effectively run away, be outside and pretty much allow the ideas to become a gas and escape my head before they create a runaway reaction and I do a Chernobyl style meltdown.
Other times, rather than the tiny space, I can breathe and open my arms out, wave my hands around inside and 'pick' certain ideas, open them out, examine the parts, stand inside them, make changes, link them with other ideas and tasks and generally tidy things up. Kind of like having a holographic model of the Death Star where you can be outside in your x wing, then zoom along a service channel until you're in through a ventilation duct and then expand it out to see each section in perfect detail.
The best I can do at work is try to get most of the shit out of my head by putting it in different places - on a huge whiteboard, in specific places where I can see myself reaching for it without needing to actually pick it up (or just do the action of reaching for it). I do a fair bit of standing and waving my arms around and staring off into space whilst stuff pings into focus and reach before sitting back down and then committing myself to text - when there are a high number of complex things all rattling around at once, I sometimes rearrange and tidy to get things sorted in my head whilst physically occupied.
Thankfully, my employers are incredibly tolerant of me and my weird ways - they let me work exactly how I find it easiest as much as possible, as when I am free to do that, complete with at least three plants, copious amounts of black coffee and limited noise from others (and I'm not expected to respond to emails instantly as experience tells them that distracting me causes issues - if something's urgent, people come and talk to me), I am productive and keep what feels like ten thousand things on the go at once. They do say that my corner gives them a fairly good idea of what it's like in my head, but in reality, they have no idea, as it's clean and orderly and meticulously labelled. Which my head certainly isn't. Although my boards can be a little intimidating when they see just how much is going on inside, apparently.
Everybody posting who describes what, to me, would be a relatively clean space in their heads with just a few things to untangle or put away - you are so bloody lucky. I wish my head was as tidy and quiet.