Some days the words flow, the scene materializes and you are on a roll. The sentences flow. Writing dialog is effortless. Some people call this “being in the zone.”
Treasure these moments and use them to the fullest. Especially while you are writing your first draft. The best way to stay with this flow is to keep writing.
All of a sudden, you can’t remember the right word for—the curved arch over the nave in the medieval cathedral, the automobile from 1947, the part of the saddle the heroine grabs—it doesn’t matter. I use what I call “zero words” the way zero serves as a numerical place holder. For example in the above situations the phrases might be: cathedral ceiling part, 1947 auto, part that goes under the horse. I put parentheses around the phrase and keep writing.
Another writer I know color codes these phrases and words. For me, that stops the writing flow. I can go back to color code for various types of research when I do the first draft. Then I can systematically do the research involved to put in the right phrase.
Your quandary may be as simple as the correct descriptive word. As you write you wonder what is another word for phoenix? You just used “phoenix” two sentences ago. You do not want to feel repetitive. Don’t stop to think about it now. Do the same thing. Use parentheses or whatever quick symbol you have and go back later.
Recognize the times when you are “in the zone” and keep writing. You can come back to the fixes.