It's not voluntary and it's not exactly healthy or as wonderful as it sounds. I'm not sure if I've truly done this to the extent that you are talking about, but I've been able to do this to the point where the room starts fading a little bit and I start to daydream. I've only been able to do that when I've been kept in a triggering environment for days on end. It's like a natural defense mechanism my brain does when I'm excessively anxious for an extended period of time. It can also be kinda difficult to break out of that numb state and feeling numb for a long time is not good at all.

If you want something that you can control, lol ativan. Get a nice strong anti-anxiety pill and your emotions just kind of vanish. I'm not at all advocating abusing prescription drugs. I'm just saying you can't exactly conjure up a dissociative state without it being pretty upsetting.