My parents divorced when I was young. I lived with my mom and sometimes would visit my dad during the summer for a week or two weeks.
One year, I spent a month with my dad, and took a plane to go back to my mom. When I got off the plane, I didn't see my mom. She was there waiting, but she had gotten a haircut and was wearing new clothes. It was such a strange feeling, because my sister clearly recognized her, but it didn't feel like she was my mom. Even after I understood that she was my mom, something seemed really wrong.
This was over ten years before I heard about prosopagnosia.
It also feels really strange when someone comes up to me and says "Hi" to me and I think about every place that I might have met this person, and until they say something specific I have no idea who they are.
I have a job as a computer tech at a school, and a few months ago there was someone who I knew was going to come in and do some work on the phone system. I had spoken with him face-to-face twice during the previous week. I needed to give him some specific instructions about where to install a telephone jack, so I asked the assistant principal to ask him to come to my office when he came to the school.
Later that day when I was in the hall, he said "Hi" to me. I had no idea who he was, and I didn't realize it until the next day when I mentioned to the assistant principal that he hadn't come to talk to me and she told me that he had been at the school on the previous day.
Also a few months ago, I was checking out of a store, and the checker said my full name without me showing him identification or a card. I had no idea who the person was. It was a person who had been probably the closest thing I had to a friend when I was in high school(the only classmate in all of middle school or high school whose house I had been to, and we had had almost every class together for a year). And I don't think he looked different. I just had no idea who he was, until I looked at the receipt and saw his name. I remembered his voice immediately and so knew that I had known him, but I had no idea who he was.
Another problem is that I think that people are someone I know when they're really not.
I often look at a person for a really long time thinking "Is this my cousin?" or "Is this my sister?" or "Is this <someone who works at the same workplace as me>?" They almost never are, but it happens a lot.