I've been doing EMDR for a little while now. Though I have weekly appointments with my T we do not do EMDR every week, though I think he'd like to. I'm incredibly good at avoiding it in any way despite knowing it will help me. I'm terrified of the thoughts and feelings it brings up so, like a child, I avoid however I can. Childish, know.
Anyway, for what it's worth, I'm always afraid that I'm doing it incorrectly though that may come from my constant fear that I can't do anything well enough. But as my mind jumps around to different things, I'm almost afraid to mention them when he asks me "what came up?" because they seem to have NOTHING to do with the situation I'm trying to focus on in the moment. Like you, random things come up and just don't know what to make of them so I assume that like everything else, I can't seem to accomplish this correctly either (insert eyeroll). My T has assured me that 1. what seem like random things WILL pop up. It's simply part of what the brain does during EMDR. and 2: What seems random usually isn't. It's connected......somehow, even if you can't see how yet. And then tells me that like dreams and REM sleep, not everything HAS to be literal. Some things could certainly be symbolic in a way because its touching not just events, but how you FEEL.
As for the numbness: I find I'm pretty darn numb after intense sessions. I feel incredibly "out of sorts" so to speak for the rest of the day. And for 24 hours after that I'm an absolute emotional mess. Feelings just spouting out everywhere. I sometimes wonder if the numbness is just a part of shock from feeling the things I've tried so hard NOT to feel for so long. And then for a day or so it's like someone opened a faucet that has been corroded for years and now there's just icky stuff pouring out of it.
I don't know if that helps you but I hope it does. I DO believe EMDR can help me. But its definitely a treatment that produces unexpected feelings in it's aftermath.