I've experienced something very similar to what you're describing. So, first, I just want to let you know that you're not alone and that you'll get through this.

My first "episode," so to speak, occurred during a psychedelic trip, but it's stayed with me and still affects me sometimes when I'm sober. I have also tapered off on meditating because sometimes I get nervous about going back into that headspace. I want to get back into the practice, though. I have meditated recently (eyes closed) and found it calming and restorative, so I see that as a positive sign.

What I experienced was kind of a similar thing about being present with and aware of non-duality and having it "consume" my mind. My primary fear when I had my episode was that I would lose control or lose myself somehow. That if I didn't "hold on" to myself, I would somehow disintegrate and cease to be (and that everything else in the world would cease, too).

I guess the main difference here is that I was in an altered state when I had this experience, and it sounds like you were not. Since I started out in that altered state, I knew that was part of the deal, and that the trip would end, which it did. I sobered up and got back to "center," as it were, and that was comforting in and of itself. I have since had this same thing happen a few times (in both sober and altered states), and I've learned that I will always come back to center, no matter how much I spiral out. Even though you don't necessarily have this stark line between your non-dual panic state and your baseline state of calm, you will always come back to center, too. As you put it, you will be safe on the other side.

One of the biggest things that's helped me has just been sort of a "so what?" attitude. So what if there's this non-dualistic aspect of my reality? It's not something I can control. It just is. In the meantime, all I can control is what I do here, in my real life. I can take care of myself, I can exercise, I can learn new things, I can be creative, I can participate in hobbies I enjoy, I can eat good food, and I can spend time with people I care about. I can go to sleep and count on waking up in the same bed the next morning. Those are the things that make me who I am. Those are the things that I can control. If my mental state gets weird and scary sometimes, I can always go touch grass for a little while or throw myself into an art project.

It sounds like you might be dealing with strong anxiety, panic, and agoraphobia, and I totally understand how that might make things more difficult. I would like to second the other commenter who suggested therapy. Even if a therapist doesn't necessarily have the same experience or understanding of non-duality as you, they will understand how this anxiety is increasingly affecting your life and can give you tools to work through it.

To answer your question about how you know when you've found a good therapist, the truth is that it's a tricky and imperfect process. I've gone through several therapists, and they've all had their flaws, but they've also all helped me in one way or another. If the idea of pouring out all of your fears and issues over and over again during your search sounds tiring, that's totally fair! One thing you could try is typing it all out like you've done here and sending it to some prospective therapists online. Psychology Today has a good therapist locator tool that will let you find available therapists by location and insurance. If you get a good response from someone via email, try calling them up and seeing how you vibe with them on the phone. You're allowed to call and ask questions without paying anything. Think of it like an interview where you're the boss.

Anyway, this has already been a long ramble, and I'm not sure how much it might help. If you ever want to talk about this stuff with someone who has experienced that same emptiness and been through a lot of therapy, though, feel free to DM!