Here are a few examples, from real dreams I have had [listed under the name of the dream, linked to my dream journal]:
Office Under Siege
I considered it "normal" because I got false memories of being a cop, being older than I actually am, and that "there have been problems with guns lately" (I'm referring to the semi-automatic fire on revolvers).
Invasive Nature
I considered this one totally, absolutely normal because I gained fake memories of a military government taking over Australia, and funding a corporate scientific firm to develop a virus that turns people into zombies. Only reason I didn't go lucid.
Pirating Teevo
Pirating Teevo is an especially unusual one (because it's more normal, the fake is hard to tell from the truth anyway). I gained memories of playing around with Teevo for months until I managed to find a way to pirate it.
Last one...
The Hunter
In this one I gained at least a years worth of memories. Memories of being accepted into the military, memories of being hired by this private sector of the government, memories of relationships. This one was especially hard to tell from waking life, as unusual as it was. Because of the memories.
As you can see, fake memories can seriously play you, making lucidity harder to obtain. It's one thing noticing something strange, then realising its strangeness. Its a completely different thing when you're brain is working overtime to explain it in the most intricate details.