These are in no order of importance or sequence, except for the last one. It should come last.
First thing, take the weekend off. This coming weekend you are not allowed to do any research, write anything, or think about your thesis. Do something you enjoy. Binge read a book for fun (and I mean for fun. Nothing related remotely to your topic or field), go for a hike, explore a city within driving distance, just leave your thesis and go do something. Do something non-thesis writing you would do.
And related, hang out with friends. Don't talk shop. Just hang out and laugh and laugh and laugh.
Second, talk with a trusted advisor. It doesn't have to be anyone in your field. Almost all researchers have felt what you are feeling. Just talking with someone who has gone through the dark night of the researcher's soul helps.
Third, talk to a counselor. Burnout is very common. Counseling can help.
Fourth, get enough sleep (if you are not doing so already).
Fifth, eat well. Tone down the caffeine.
Sixth, go exercise.
Seventh, if you have done all of the above and whatever your trusted advisor and/or counselor has suggested be real with yourself. Take a year off. Figure out if a PhD is the right path. It is not for everyone. And that's OK. It may not be the right time, the right subject, the right research question.
