Thanks!
A couple of mine were already mentioned, but they work well for me also.
I was going to add, and this was a pretty big one for me: put on some tunes. Preferably something that you love but haven't listened to for a while.
Not everyone likes music in the shop, and some only do sometimes, but I find the right rockin' tunes playing can really help pull me out of a slump.
I'm usually so busy just trying to get work done that I can't be bothered trying to put on music, but it really can help sometimes.
Another thing I wanted to add... I go through "waves of engagement" with my customers, not on purpose, but just I go through phases where I am super busy and burned out on dozens of daily emails.
I've found that touching base with past customers or those waiting on projects, they can often be very excited about their own project or desire, and that excitement is extremely contagious.
Sometimes a single excited email from a customer is enough to pull me out of a bad slump.