According to Medical News Today, most people can recall a time where events, faces, or places from their waking life creep into their dreams. But unlike the day-residue effect, which replicates recent events like a hectic workday only a few hours later, dream lag can show up a week later after someone’s first experienced it. That’s because it can take a couple of days for some experiences to be processed by the brain and filed away into your long-term memory.
Once it’s there, bits and pieces of the memory can work their way into your dream, leading to a déjà vu effect that almost feels like the real thing. The chances of this happening are even more likely considering that 65% of all dreams are based on daily occurrences in our lives, according to a 2019 Sage Journal study. Not to mention that depending on the quality of your snooze session, it can even bring on a lighter stage of sleep where these dreams can happen.