I know that Uny would say, if you're very concerned and feel that going to the ER is the best thing, then do so. They may be able to rule out what it isn't, but may not be able to tell you what it actually is. The only thing is (and I have never been hospitalized for heart issues) but I know that they will most likely give you drugs of some sort, to calm you and/or bring blood pressure down etc.
I wouldn't try anything else right now no essential oils you may be allergic to, no supplements. Did you try a warm water enema yet? It may help relieve whatever it is if it's something your body is trying to release or is allergic to.