Can you go hold some ice? It may help you ground.
Try to not panic about the dissociation (I know, really easy to say...).
It is extremely uncomfortable and even scary, but you are real and you are all here and it will pass. The calmer you can help your body be, and the more connected it to this moment now that you can be, the sooner it will pass.
And it will pass, even if you do nothing at all. Eventually, it will pass.
You can also try counting everything that is blue around you, then everything that is green... Just one way to try and ground through mindfulness.