I'm not sure if I've had triggering dreams that were unrelated to my past... I've had nightmares that left me feeling off much of the following day, and I've had dreams of the past that would leave me feeling drained and triggered.
Both of those effects generally last well into the following day, if not several days (in the case of memoirs or flashbacks in dreams).
It's frustrating and debilitating. I often can't focus on anything else.