Should you make a special notation in scene headings that are flashbacks or dream sequences? If so, how?
If the flashback is a single scene, then [FLASHBACK] is generally added to the end of the scene header, like this:
EXT. LOUVRE – DAY [FLASHBACK]
If you have multiple short scenes clumped together in a flashback sequence (for instance, the location is changing, but the time-frame is the same), then you can use [FLASHBACK] for each of those scene headings, or maybe [FLASHBACK, CONT’D].
When in doubt, just use common sense. If the flashback is really another sequence in the movie, like the three chapters in GO, then don’t put anything in the header.
The same logic applies for dream sequences, e.g. [DREAM SEQUENCE], with the caveat that sometimes you don’t want the reader to know at the head of the scene that it’s not real. So obviously, you wouldn’t put the tag there at all.
In general, try to read the script as if you didn’t write it, then see what’s clearest.