I quite enjoy the task of writing and testing code, but spending too long without a break can be tiring. In reality, I'm not working 100% all of the time, I'm flicking between windows (GitHub, Slack, social media, code, documentation).

Sounds like your brain tries to tell you, in a manner of subtlety that's so exemplar of it, to take breaks. Why else would you want to distract yourself from something you enjoy?

Whenever there's something I can't solve, be it a story turn or a piece of code I need to achieve the result, I get up and go to bed. I lie there, and the solution - or, at least, the next step - comes naturally. I think it's because my bed is a place of comfort, so yours might be different.

When I need to force myself through studying something I don't like, I use Pomodoro timers. I set one up and go through the material until the break comes. During the break, I think of nothing related to the material and only switch back when the work alarm rings. This forces me through the work in a surprisingly pleasant manner. This takes its mental toll, though, and I only use it for especially hard cases, but if I have to do something, that's my go-to method.

And when I feel stuck on something completely, I leave it for later and turn my attention to something not work-intense, like cooking, cleaning up or walking. Rest is as important as work.