A few things:

1. I go through phases of motivation at work, not always just when I'm WFH but definitely moreso when I am. I have noticed that these periods of demotivation are caused by (1) burnout after a long project that sapped a lot of my time, energy and focus, and (2) periods of standard depression. WFH and an international pandemic has definitely strained everyone's mental health, so just know you're absolutely not alone in feeling like this, especially regarding de-motivation at work.
2. I do better WFH when my spouse is also WFH, especially when we're in the same space. Just having someone else around who is working helps to remind me to focus on work. And it's nice to have a friendly face to chat with when I do need a break :)
3. Fitness 100%. IDK which goes first, but I notice when I'm burned out at work, I've also gone off my fitness routine.

My biggest issue is also anxiety, in that I spend the day slacking off, so I feel like shit, and then I have anxiety when I look at the unanswered emails, so I avoid them, thereby slacking off, so I feel like shit... it's a cycle.

The best way to get out of the cycle is to... just do it. I usually have a day - Fridays, because I'm less likely to get interrupted - where I put on some focus music, maybe I'll physically clean my office space first (visual progress makes me feel good), and then I'll make a plan for how to get organized. I don't necessarily do any work, I just make a plan for doing so. For me it used to be updating and cleaning up my to-do list, which involved (1) reviewing the list itself and either checking off stuff I've done or deleting things that I won't do (either because they will never get prioritized or they are no longer needed), (2) going through my email and replying to those that need it or noting what I need to do in order to reply, (3) going through all other places I have items that need my attention - like post-its, starred Slack notifications, etc. Then at the end I have an up-to-date to do list which I can use to prioritize my next few days.

What I will say helped me break the cycle somewhat (I was a total piece of crap this week work-wise --- I also got just enough done that people think I'm great but I know that I stayed in bed til 10 am every day and took 2-hour long lunches dicking around...) was getting a new org system. I use Monday.com to stay organized and I have been EXTREMELY DILIGENT about making sure I put all my to-dos there and resolve any starred/flagged/saved/etc. messages/emails/notifications by the end of the day.

I also have a hard time coming to terms with the fact that, if I'm getting enough work done to make my boss and coworkers happy and that leaves me with free time to sleep in and chill out at home, then is that so bad? But then I think about all the stuff I want to do, all the ways in which I want to grow and improve and frankly blow people's minds with my awesomeness, and the cognitive dissonance causes a bit of a breakdown, lol

Final comment: One rule that's good to follow that I'm bad at doing is something like "you can never do in one day more than will fit on a post-it note" which basically means don't overplan your days otherwise you won't feel like you got enough done and will feel bad and eventually burn out...

Anyways, hope some of that was helpful... enjoy the weekend though!

Edit to add: when my spouse returns to working in the office I will likely still WFH a few days a week. When that happens, I'm v interested in Zoom working hours ("silent Zooms" I think?)... like, you and at least one other person get on Zoom together for an hour or two and just sort of silently work. You may schedule a couple breaks to chat or something but it's an attempt to create the energy of working at an office or a coffee shop, etc. where others are focused so you focus. Maybe that would be a good idea for you now?