Prabin
 diabetic chocolates probably aren't harmful, but as has been written, if it contains polyol sweetener, and you are sensitive to it, you could develop diarrhoea. 
A small amount doesn't actually affect me at all.
 However it doesn't taste particularly nice and costs a lot.
 High cocoa solids dak chocolate is often lower in sugars. LIdl do a 74% one which is 33grams of sugar per 100g. Others are lower. Then Just hav a LITTLE bit. 33% of one square isn't a lot of sugar in total
 Hana
 PS a TINY bit of almost anything isn't going to destroy weeks of carb counting.