I’ll join in! DH and I are independent consultants, running our business out of our house. I have just been DONE for a couple of years. In my case, a lot of my dissatisfaction stems from the low quality of architectural drawings I have to work with - I swear, they’re getting worse and worse. And when I dare ask questions about the “cartoons,” people get annoyed. But we’ve got debt with the two kids in college so we have to keep working. Blech.
Simple solution. “Boy toy.” 
Ok. Working sucks. Don’t let it define you. Make sure your doing other things you like to do. Make time to take off - long weekends and such. Work will always be there and the current project is never as important as people make it out to be. Good luck.
Start listening to the podcast “Side Hustle School” The daily podcasts are short and even if you’re not looking for a side hustle, the ideas and comment may help you work through where you’d like to be and motivate you
So many times DH and I talk about throwing in the towel! It’s rarely our employees that cause us to want to quit but more often customers. We quietly listed our business for sale and any decent offer gets it.
I understand how you feel. Our situations are different, and I’m a few years older than you but the burn out is real. Honestly, I have a good job and I am well paid but I’m over it and have been for some time. There are reasons why I feel the way I do but it isn’t worth getting into it. I’ve worked full-time my entire adult life and I’m exhausted. I feel like every time I walk into the office a piece of my soul dies.
The horrible thing is that between raising 2 children, working full-time, taking care of a house and a husband who is less than helpful, I don’t have hobbies or free time and I’m overwhelmed and again, exhausted. I feel like what I really need is a sabbatical or something where I could step away without giving up my job, seniority, benefits, etc. I’ve been so busy “doing” I haven’t had time to think. Our youngest graduates from college this year and so will be empty nesters. The big question is now what???
I’m to the point where I probably have about 7 - 10 years left to work and honestly, I may as well stay here. I’m not going to start over somewhere as the new girl at this point in my life and there’s no point in walking away from my salary.
I could go on all day…but yes, I understand completely that mid-life professional crisis.
Another perspective might suggest that your rates are too low. How would you feel if your compensation was doubled ?