So I am not a medical professional and I don't want to tell you something incorrect, just keep that in mind.
But I think they can hold you there, even involuntarily in some cases. I'm not sure what criteria have to be met for them to be able to do that, or how often they actually do it. Just because they can doesn't mean they will. There must be some information online about what the ER could or could not do if you decide to go in, and the laws could depend on where you live. Many factors will influence that (potential) situation, and I am not informed enough to give an adequate answer. If it were ME, I wouldn't take that risk. It would take an hour to explain how that final loss of control would be more damaging than anything else to me, but I won't put anyone through reading that. That's just me, and this isn't about me. It's about you. (My opinion is VERY biased on this topic because of previous life experiences and a deep mistrust of doctors lol.)
As for you, what options do you have? Is it possible to take half of your dose in a day? Your psychiatrist should be able to adjust your meds/dose without involving the ER though. It's psychologists that cannot prescribe medication. There are crisis lines that you can call and talk with someone if you think that would help. Sometimes words are not enough to take away the feelings or make the numbness recede.. it may come down to someone staying quietly on the line with you, just being there. This response feels inadequate to what you must be going through, which I can't imagine, and for that i am sorry