I experience lucid dreams from time to time. Sometimes I have trouble recalling past events and being able to distinguish them from lucid dreams. For instance, On my drive home from spending the weekend visiting friends, going out to the bars and meeting a lot of new people. I shook a lot of hands, heard a lot of new names, and met some new girls. I had a dream on my second last day there, about meeting people in this one particular bar. There were girls and dudes and everything was very lucid and completely seemed real. Now, I think at some point in the dream I shook hands with this one person but it was like a hand slap with a snap, turn, slap, slap, slap, slap, fist bump, explosion. It was complicated but somehow we both new it. On my drive home I really had myself convinced that was something that happened in reality; thinking, probably when I was drunk and my conscious was a little hazy. Maybe it was just the alcohol but Its not the only time a memory of a lucid dream presented itself a real life past event in my mind. I can usually work it out that it was a dream but who knows what if some of my memories of real life are actually dreams.

It could definitely be due to having been drunk or even just overtired.

That happens to me once in a while; I'm not sure if something happened in the past or if I only dreamt it.

If this happens frequently and causes you to feel very confused, like you aren't always sure what is real (I don't mean in a philosophical sense; I mean that you really aren't sure if the things you sense are real or just part of a dream/hallucination), or if you aren't sure about important things, like whether you showed up at work or at school, see a doctor, as it could be a symptom of something more serious.

you should remember whats your dream and real