The purpose of an expiration date is so that a product can be consumed while it is at it's peak in flavor and nutritional value. Most foods can be consumed well after the "expiration" or "use by" date. As non perishable food ages, it can loose some flavor, it's nutrition value and appearance.
I have had baker's chocolate in my cabinet for two years. It developed a chalky finish, but it still has great flavor and is not rancid, so I used it, without any consequences.
You will not get sick from eating chocolate. However, if you ate a bunch of chocolate on an empty stomach, you could very well feel a little nauseous from all that sugar in the pit of your empty stomach.