A manual for writers of research papers, theses, and dissertations, 7th edition - Kate L. Turabian 2007

Manage moments of normal panic
Engaging sources
Part I. Research and writing: from planning to production

This may be the time to address a problem that afflicts even experienced researchers and at some point will probably afflict you. As you shuffle through hundreds of notes and a dozen lines of thought, you start feeling that you're not just spinning your wheels but spiraling down into a black hole of confusion, paralyzed by what seems to be an increasingly complex and ultimately unmanageable task.

The bad news is that there's no sure way to avoid such moments. The good news is that most of us have them and they usually pass. Yours will too if you keep moving along, following your plan, taking on small and manageable tasks instead of trying to confront the complexity of the whole project. It's another reason to start early, to break a big project into its smallest steps, and to set achievable deadlines, such as a daily page quota when you draft.

Many writers try to learn from their research experience by keeping a journal, a diary of what they did and found, the lines of thought they pursued, why they followed some and gave up on others. Writing is a good way to think more clearly about your reading, but it's also a good way to think more clearly about your thinking.