As a software engineer, I'm often working on code that other people have written a long time ago. Sometimes (more often that I'd like to admit), I don't understand that code, or the reason for that code. The phrase "my code works and I don't know why - my code doesn't work and I don't know why" is not just a meme - it's reality!
In every profession, there are moments when nothing works. You can't focus. Every solution you come up with for a problem fails. You are waiting for answers from your co-workers to solve a problem, but you can't stand to do nothing while you're waiting and are still trying to solve the problem in vain until someone answers your questions.
You're starting to get frustrated and realize that you can't get a grip on anything. No matter what you're trying to work on, you hit a wall. Nothing works. The universe hates you. In this mode, you're making decisions based on emotions instead of rational thought (this is called the "affect heuristic"). These decisions are likely to be wrong, which causes a spiral into more frustration and even more wrong decisions. This is why it often feels like "nothing works".
As knowledge workers, we can respond to a situation like this in a way that other professions often can't: we can take a step back from our work to take a break. Especially with the new normal of remote work, we have the oppurtunity to take a break pretty much any time.
How often has it happened to you that you found the solution to a problem (or at least an idea for a next step towards solving it) while taking a shower, walking the dog, or doing something else that was completely unrelated to the problem? That's your unconscious mind working on the problem while your conscious mind is recharging its battery.
By taking a break, you can reduce your frustration level - increasing your chance to make correct decisions again - and at the same time give your unconscious mind a chance to take a crack at your problem. I'd say that's a valuable use of time.
Here's a catalog of some things that you can do when the universe hates you:
Switch to a different problem. Instead of running against the same wall over and over again by trying (and failing) to solve the same problem all day, switch to a different task. Your unconscious might decide to continue to work on the problem and come up with a next step towards solving it. If you notice that you're getting frustrated, though, and it affects the new problem as well, you should probably take a break.
Do some shallow work. Give your conscious mind a rest by doing some shallow work like reading emails, answering chat messages, or filling out your time sheets (although if your company's time sheet system is as bad as the ones I know, it might not do anything to reduce your frustration).
Take a walk. Walk around the block. Let your thoughts wander. Listen to a meditation program, podcast or an audio book. Or listen to nothing at all, to give your subconscious more space to solve your problems for you.
Work out. I know that you're not working out enough, so you might as well make use of your unproductive time to do something for your body. Create a list of exercises beforehand so that you don't have to spend energy making the decision which exercises to do when you hit a wall.
Cook something. Take an hour off to cook and eat in peace and quiet. I usually don't enjoy cooking much, but when I put some loud music on the speakers and I'm looking forward to a tasty dish, it becomes an enjoyable use of time. And I'm even doing my family a favor.
Read a book. Reading is a very peaceful activity that can replenish your mind. A fiction book can take you to other places, shutting off your conscious decision-making mind for a time. A non-fiction book can inspire you with other people's thoughts, activating your mind without sapping its reserves. I often feel replenished after reading a chapter or two.
Take the rest of the day off. If nothing works, take the day off and focus on the little things of life for the rest of the day. Clean the house, tidy up your working space, or fix the lawn mower. These tasks will let you feel you achieved something, after all. Or indulge in video games. Whatever takes your mind off things, so it can recharge.
Add your own ideas to this list pick something from it each time you're stuck. Make a habit of unblocking yourself by letting your mind wander.