Give yourself permission to do nothing. Many people do this by using words to give their version of "nothing" meaning - for instance, you may have been meditating. I know that some people attach extra meaning to the word "meditation" that makes it seem active but the reality is that it's little different that watching a fire or a snowfall - you're allowing your mind to be blank, or to run wild, or to be ignored, or, etc, etc, etc.
So stare at that wall and don't worry about it. No need to feel guilty. Perhaps later you'll regret it, but that doesn't mean you should feel anxiety now for a future feeling you may or may not have. In some belief systems detaching yourself is important for a variety of reasons, but one thing it does for you is allows you to get rid of the anxiety and regret by accepting your actions have value, even though in your current culture and society or upbringing that value may be minimized.
Who cares if it has extrinsic value? If you accept it, then it's as valuable as anything else you might do.
If that still bothers you, then perhaps what your mind wants is to perform an act of creation, rather than consumption. I know that often fills a void for me when none of the entertainment options available are enticing. I don't know what you might do to create. Writing, artsy stuff, even just playing with paperclips and magnets might be enough. Make a plan for a future vacation (even one you might never take) including cost, things to do, etc can be creative. Cooking.
If that's not it, physical activity might be needed - perhaps what your body is missing is the normal level of physical activity your job requires, and a short walk might be enough to get back in the groove.
But personally, I'd put on a video of a fire or snowfall if you can't have a real one, grab something yummy to drink, and just relax, sinking into the nothingness of nothing.
