Freelance burnout tends to build quietly, since there's no manager or team to notice it from the outside. A few early signs worth paying attention to: dreading opening your inbox, taking noticeably longer on work you'd normally do quickly, and saying yes to projects you'd normally decline out of a vague fear of saying no.
The structural fixes tend to matter more than willpower. Look honestly at your actual billable-hours load against your rate calculator numbers, if you're working far more hours than the math assumes, either your rate or your workload needs to move. The take-home pay tool can also reveal whether you're overworking to compensate for underpricing.
Build in real breaks between projects rather than back-to-back scheduling, even a few buffer days meaningfully reduces the always-on feeling. And if a specific client relationship is the source of the strain, it's worth reading the when to fire a client guide, sometimes the fix isn't more rest, it's fewer of the wrong clients.