One of the many obstacles I've had to overcome is burnout. This happened to me many years ago when I was writing more than I was resting. I remember distinctly something in my head giving way and looking at the screen as if English was a foreign language. After that, I struggled for months trying to put sentences together, copying existing work more than writing new text. It was very much like that Twilight Zone episode where the meaning of words shifts and the main character suddenly finds everyone around is speaking a language that makes no sense. We see him at the end of the episode relearning basic vocabulary so he can talk to people again.
It wasn't quite so bad for me, but it was bad. I had a job to do and I was unable to do it. Worse still, I couldn't (or didn't) tell anyone because I was afraid of losing that job. The fear didn't help; in fact it prolonged the problem because I had to suffer silently and try every trick I could think of.
The good news here is that brain research shows the elastic nature of this most amazing organ. Patients who suffer brain damage as a result of stroke can and have gone on to relearn and regain lost functions. So too, after some years, I found that writing easier and natural again. How did I do it?
It was a lot of work. I resumed writing in my journal, which I had stopped some years before. I read a lot too. Reading helped more than writing. I read non-fiction mostly; I don't know why. I also read books on writing, ironically, and a few self-help books. These books led me down paths not-quite-so-dark as the one I was on. Slowly I got by; I even changed jobs and found working with other writers helpful.
The moral here is to feed your creative processes. Read regularly. In the development stages of a project, write 1000 words a day and then stop. Also stop if you are tired after writing for an hour or more. Brainstorm for ideas regularly too. This should be more like play while doing useful work. And above all play and rest in whatever form works for you.
For me, the ideal day goes like this: I get up and start writing. I do this because I know I am best in the morning after resting overnight. I'm a morning person. If you are not, then write in the evening. I review a little of the work from the day before and then add to it, writing 1000 words or until I feel drained. Usually that takes all morning. In the afternoon I read, either a novel or something thought-provoking to generate ideas. After an hour or two of reading, I rest, play with the dog, handling the chores around the home, do errands, whatever needs doing. The next day I repeat the process.
If I am not actively writing but editing then the workflow is different. I read and edit until:
a. I get tired and know I can't edit anymore.
b. I see I have lots of edits and I really need to revise and rewrite. Editing alone won't do.
Notice in the both workflows that I watch for internal signals to tell me I'm done. It has taken years to recognize these signals but they are very important because there's no point trying to write or edit if I'm unable to do it well.
So take care of yourself, both physically and mentally. The writer is like an athelete; he or she trains for years and has to perform to achieve. He or she has to rely on cues from the body and mind to know what works for him or her and what does not. So pay attention and happy writing.