I've done this as well. Either emailed him and said what the specific thing was or just said something like "I need to talk about a certain thing tomorrow, but am anxious about it and worried what you'll think of me. Can you help me bring it up?"

I've also checked in with him before after a session where I shared something that I felt embarrassed and/or ashamed about, asking something like, "Are you still OK with what we talked about?" And he'd simply reply "All is well on my end." And that helped.

If email isn't an option and you're meeting in person, you could hand him something saying that at the start. Or if you're remote, you could type it in the chat (if the program offers that)--I did that once on Zoom for something I was ashamed to say out loud.

I think it can definitely help to say right at the beginning (or in an email/note) "I'm afraid this is silly and that you'll think I'm an idiot" (to use your words). Then your T is likely to reassure you or at least to be more gentle.

ETA: A sort of funny story about the Zoom chat one. I really thought I hadn't told my T about this one detail before and was making this big deal about "I'm worried you'll judge me and think I'm disgusting." When...apparently I'd already told him a couple years ago! I must have completely blocked it out.