Dreams come from events of the last 36-48 hours
Based on my experience, most of the “noise” in dreams comes from events in the last 48 hours. For instance, this morning I had a dream with two of my sisters. One sister had just climbed a ladder up to our second story hotel room, and then we saw Karl Malden downstairs.
With that I began thinking, and woke up in the dream. I said, “Wait, wait, wait, it’s 2014, he was on tv back in the 70s, and he was fairly old then, he must be dead by now.” Then I remembered that I saw something on tv on Saturday while I was flipping through the channels that reminded me of The Streets of San Francisco, and I really knew what was going on in the dream. (And I only stayed on that channel for like two seconds.)
So, again, a lot of dreamstuff comes from the last 48 hours. (Of course after that I realized that I wasn’t really in a hotel room and those weren’t really my sisters, but that's another story.)
(This is a note I posted on Facebook on December 8, 2014.)