According to dictionary.com, "A trigger warning is a statement at the start of a piece of writing, video, etc. alerting the reader or viewer to the fact that it contains potentially distressing material."
While nightmares are common, nightmare disorder manifests as nightmares so vivid and so frequent that they create major distress and daytime impairment. These nightmares routinely disrupt sleep patterns and typically occur in the earliest hours of the morning.
While the idea of having a comfort zone isn't exactly novel, we can expand that idea when we talk about environmental triggers (things that set off immediate red flags in our minds). One way to more effectively describe overwhelming triggers and their impacts on our behaviors is the "window of tolerance" in which we most effectively function and perform. This is where our A-game fight emerges.
That's like being asked to identify the critical features of bigfoot based on a grainy photograph that's also suspiciously confusing and difficult to discern.