Hi Katybug!
Welcome to the forum!
I was in that state just a couple of hours ago. It's a dissociative state. It's something we do when we feel overwhelmed or have been triggered by something. It's a very primative survival tactic, that can be awfully inconvenient - to say the least.
Satvea has good advice, particularly if you're currently in a bad, or dangerous situation. If not, if you're safe, then I would personally add a qualifier and have to say that the ER can be great for many things, I don't think (unless you're in very dire straits) you'd have to go through the stress of going to the ER for dissociation. Unless you're fortunate enough to locate a fantastic trauma center with good staff experienced in helping people with traumatic issues/PTSD, they usually wouldn't have a clue as to how to help you get out of a dissociative state. (I find ERs to not be helpful for PTSD issues, unless someone is suicidal.). If you can go directly to find someone to talk to in the hospital's social services or chaplain's department, that would save you from the anxiety-promoting ER waiting room/ dept.. ER staff would want to push you out quickly, especially if you're not visibly injured. Chaplains and Social Services are usually ready to sit down for a caring, calming chat.
A phone call to a crisis line might be easier on you, if you need someone to talk to.
I'm not a Dr., just a fellow-sufferer, but to me, you don't sound like you have derealization, at the moment. If you wanted to further nail down a name, depersonalization traits are showing in your description, but I really wouldn't want to get hung up on that - the inclusive "dissociative state" or "dissociation" name works just fine. People who know trauma will get what you're saying.
The best methods for getting out of this state lie within your own capacity to re-emerge.
The quickest way is to "Get Present".
You look around you (noticing that, in the moment, you are safe - if not, leave, and go to a place of safety).
You can say to yourself, or aloud, things that you notice, colors, what is going on outside.
How is your body feeling? It helps to take a drink of water, slowly, noticing every detail that you can about what it feels like.
Petting an animal really helps.
Going outside and looking at trees in detail, flowers, birds, the color of the sky, the beauty and movement of the clouds, etc...
What do you smell? You can cut a piece of fruit, smell and taste it, noticing every tiny detail.
Distracting yourself:
Eating, exercise, watching a favorite or funny movie,...
Many others here can give you further examples of how to ground, get present, mindfulness, somatic experiencing, etc...
I've not read your intro yet (apologies, saw this thread first and wanted to help). I hope you're currently in therapy, with a trauma counselor.
My heart is with you!
Deer