Do you ever have a "new" memory?

Like, all of a sudden you have this recollection that you've never had before. But it feels so real. Like of course that happened, but how come I never knew about it before? It's almost like someone is travelling back in time and changing the way things that happened and the memory is just kind of added. I don't know, I feel like I'm not explaining it well. It happens literally ALL the time to me, though. I don't even trust my own memory half the time anymore because I'm afraid it's just making things up and trying to trick me.