Do you have any means available to calm yourself down? It sounds like it could be DOB-dragonfly you ingested. Something like a benzo could give relief, you know like Valium or Xanax?
Are the muscle spasms getting any better or are they getting worse? The metal taste in your mouth should not be something to alarm you, it's a side effect called dysgeusia certain drugs can have. What do you mean by frothy urine though? It can just be foaming extra from proteins getting in your urine but how hard are you peeing into the bowl exactly, is it still frothy when you do it more gently with less pressure? I think it's a good sign that you are able to pee. Apart from trying to remedy the situation by some things I am saying I'd lie down if I were you and try to relax as much as possible. Panic will only make these things worse. If you hyperventilate breath into a bag.
Avoiding the ER... well on the one hand getting permanent injuries or worse are things that are a lot more shitty than going to the ER, I would see if you got some meds on hand, call a friend and have them watch over you if you are not going to the ER, that is something of a must IMO. And if you feel things like horrible pain in your fingers and toes and them going extremely tingly then numb, then turning color thats when you should immediately seek medical attention if you insist that you are not going to seek it right away.
Get a friend, get anyone who has a sense of responsibility, anyone at all. If you cannot muster that, you might just have to call the ER after all. Or get someone to drive you to at least avoid the ambulance bill. Then you might be able to sit on watch, say that you do not want to get checked into the ER right away but at the very least be sitting on a bench when you become more certain that shit is getting serious.