AIO, looking for perspective on something strange my mom did to me

Hey, I’ve been thinking for a long time about whether I should even write this, but I’m too embarrassed to tell anyone in real life, and anonymously it feels easier.

Something my mom did has been bothering me. It happened a few years ago. I had experienced an attempted rape and went through some therapy afterwards.

I remember one day (in the period when I was undergoing therapy) I was lying on my stomach on the bed, doing something on my phone, and my mom suddenly got on top of me, sat on my butt, and started moving in a way that mimicked sex act. I was completely shocked and, I think, yelled at her for the first time in my life. She didn't said anything and left.

Since then, this memory sometimes comes back, and I can’t make sense of it. I wonder if I’m being overly sensitive and if my reaction was an overreaction, or if maybe my mom really just has a very poor sense of boundaries and did it “as a joke”.

After that event, it’s hard for me to connect with her, the fact that she did something like that after what I went throught feels really odd to me.

I’d like to ask, am I overreacting, or was it actually weird?