I feel real arousal towards my thoughts it upsets me

Hey guys recently I been facing anxiety because I have a fear that I acted on something I know I didn't do but it feels real because it felt like I had attraction and arousal to a younger photo of a ex gf I feel so weird feel so anxious I need help Idk what to do

I was with my sister today. When I look at her, sex images pop up and I have to imagine them because in a second I feel very clearly like I like it. I ignored it the whole time but it feels real and I'm not calm.

constantly when I deliberately imagine sex scenes looking at the photo that triggers me (my sister's face), it's like I'm imagining, projecting how I see myself how self pleasure myself, and I feel like I can, I have some drive, and it's like there are no limits, like the more I imagine the stronger it is... it scares me a lot, and I think I'm the only one who has it that way, and that it's not part of ocd...