I think that most people have dealt with the same thoughts here and there...

I don't think that you necessarily need a therapist for the occasional intrusive, or disassociative thought. Unless there's other factors that are leading you to muse over such things.

Maybe an apology and some reassure is called for; after blindsiding her with that nugget of information.

Express how thankful you are to have a open minded relationship with her; that allows you to express these feelings. Without all of the bells and whistles being blown out.

I am sure that your mom would rather know; than not know. It is just a surprising admission and it probably shook her up, in the moment. It's a heavy subject to talk about; even if everyone is on the same page.

So don't be too hard on yourself or your Mother. These feelings will come and go through out your life. The time for help is when you don't have it come and go..