Cough hard, several times, that helps the heart realign. Also trying to dry retch, has similar effect. Breath in slowly to a count of seven, hold for a count of seven and release slowly to a count of seven. Do this several times and it will help you calm down. (This is the same as breathing into a paper bag) It sounds like a panic attack and this should help. Not to be alarmist, but if the above has no effect, you should consider phoning NHS Direct on 0245 4647 or look at their symptom checker on www.nhsdirect.nhs.uk