When chocolate gets old it usually just loses it's texture and taste.
It's very unlikely that you would get sick if you ate bad old chocolate and if it went bad enough to make you sick then you'd likely notice a really bad smell.
I've eaten chocolates that I've forgotten about and had for 6 years before and although the 6 year old chocolate wasn't as tasty or had the really good texture to it the chocolate never made me sick.
If you're in doubt then you can just throw it out but you're unlikely to get sick at all from eating some old chocolate.
Old chocolate can sometimes grow microbes and bacteria but you'd usually notice a bad taste or bad smell to the chocolate that would make you vomit before you ate all the bad chocolate.