Is it possible to suffer a mild heart attack and not know it?

i felt a strange pain in my chest the other night and it was accompanied by dizziness and cold sweat. after a while i had my wife drive me to the emergency room at the nearest hospital and the nurse checked my blood pressure which was fine and gave me a cardiograph (a machine with wires attached to my chest, gut, arms and legs). the doctor that diagnosed me said the cardiograph was fine and that all was from muscle pain due to my job (sewing machine operator). i still feel chest pains when i lie down and this afternoon i felt numbness in my head and felt dizzy at work. could it have been a heart attack and do i have reason to worry?