Given the symptoms you report (shortness of breath, being smothered, tachycardia, throat tightness…),the normal results of the medical tests in the ER, a pre-existing condition (anxiety disorder) and reduction of the Paxil.... you might be experiencing a type of anxiety disorder, probably a panic disorder. Panic disorder often manifests with neuron-vegetative symptoms like those that you describe. Panic disorder can be treated with psychotherapy and medication, if required. You are already using one of the selective serotonin reuptake inhibitors (paroxetine). SSRI are antidepressants and the first choice among modern medicines for panic disorder because of their efficiency and the fewer side effects documented. Anxiolitics (diazepam and other benzodiazepines) are used for fast symptom relief while antidepressants are used for long term treatment. SSRI require a few months before they begin to act on the body. You shouldn’t change the dose without first consultating your GP or psychiatrist. Psychotherapy is also very important and includes cognitive-behavioral methods. You may ask for expert help from a psychologist, psychiatrist or another mental health professional.