Hey, I don't know if this is the correct subforum to post this on. If not, please move it.

Today I was alone at home (I live with my parents but they had gone to their friend's house) and I decided to masturbate. However, it hadn't even been 5 minutes since the moment I started and I began to 'feel' watched. I started to think my mother had installed hidden cameras in the room and she was watching me from her friend's house.
I knew this probably wasn't true, but it made me so anxious I had to stop, dress myself and look for cameras all over the walls and furniture. Then I called my T and told her I couldn't sleep so she recommended me a mindfulness guided meditation so I calmed down.

This isn't the first time this happens to me, it's happened a few times before.
Also, something similar happened the first time I had sexual contact (that was at my grandma's house and I thought my uncle had installed the cameras).
I also believed my mom had downloaded a KeyLogger to my laptop and would see everything I was doing when I was 11/12 and talked to my girlfriend at the time (we even invented new words so my mom wouldn't be able to understand).
When my grandfather died, I was around 10 and I thought he could read my mind when I fantasized about kissing the boy I liked - from heaven (I then became an atheist though and I don't believe this anymore) and I was very embarrassed.

My point is, I think this may only happen to me when I experience sexual behavior or intimacy.
I want to tell my therapist about these 'delusions' but I feel ashamed to tell her I masturbate.
Do you have any idea what this might be caused by? Any way to fix it?
How can I talk to my therapist about this without cringing and wanting to crawl into a hole?

PS: I've been seeing my T for 2 and a half years and I'm very comfortable mentioning almost every other topic in the world. We have a very good relationship.
Also, English isn't my first language. Sorry if I expressed myself incorrectly.