I had a sexual fantasy about my mother. Can something like this happen?

Hello doctor,

I am a young woman, and I have a question concerning sexual fantasies. I have always been sexually open, and I was never ashamed of any of my fantasies during self-pleasure. Even when I had a pretty weird fantasy like cheating or having sex with an older man, I was never concerned about that because I knew I would never even want to do that, and I was thinking it for the thrill of the taboo. However, two days ago, during masturbating, I was deep in my fantasies when I suddenly thought about my mother. It was only for a few seconds, but afterward, I felt very weird. I would never want something like that to happen because it is so gross. I usually do not mind weird fantasies because I do not take them seriously. But after that, I am so incredibly ashamed of myself. I want to forget it ever happened, and I feel so gross. Now I am afraid to fantasize because what if I have a weird thought like this again. How can I move on from this and go back to not being ashamed of myself? Can something like this happen, and I should not worry? Does that mean I am a sick person? Can you please guide me?

Thank you for the kind reply doctor,

I want to ask one more thing. I re-read my question and was not sure if I expressed myself correctly. The brief random thought about my mother was also a sexual one, but as I said, I would never want something like that to happen. Is your answer still the same? I want to make sure because I am so relieved by what you said and could barely believe how compassionate you answered, so I was a little afraid that maybe that information did not come across.