Do you ever just say fuck it and take an entire day to hang out alone? I recently started calling them "studio days" so I sound like a functional adult, but that's my fallback when I'm feeling down or uninspired. It's like Ferris Bueller's day off for an ornery millennial.
My favorite things to do on a day like that are: see a matinee movie alone, meander through an art museum, post up at a thrift store and methodically look though everything, sit at the end of a Barnes and Noble end cap and flip through a stack of books, or go to a restaurant and have a ridiculous meal alone (oysters and champagne? Don't mind if I do! Or like my girl Pia, foie and a glass of vin santo). Observe people and practice being alone without your phone or a book for support.
The list could go on and on, but the important thing here is the lack of hastiness; no hustle and bustle. You'd be surprised how quickly you get the pep back in your step when you stop obsessing over your problems for a few hours.