That happens to me all the time. Anytime I dream a memory, I'm not so sure about whether or not it is real when I wake up. Extreme "memories" like the one you had- well after a couple of minutes in the dark I shake myself awake and realize it was just a dream memory. But mundane "memories"- sometimes I have to ask people about it to be sure.

It's interesting to note that when something actually happens as the plot of the dream, then I never get confused if it is real. The problem arises (like in your case) when I dream that I am remembering something. Only then am I later unsure if the memory was something real that I remembered in a dream or just a part of the dream itself. It's very confusing, especially when it is something boring. For example, I dreamt recently that my grandma and I were watching a funny movie. We laughed until we cried because the movie was so funny. Then my grandma said, "remember the time you and your brother were laughing so hard that he started crying and we thought you had teased him and upset him?" Then we laughed some more, then I woke up. The next day I was wondering, did it really happen that once my grandma thought I'd made my brother cry? I can remember this memory so vividly but I don't know if it was real or just in the dream.

This happens to me all the time. I'm going to be a senile old lady.