Why do i crave sugar?

im not talking about your average, "oh i think i want a candy bar"scenario. i have times where i will eat anything with sugar.any candy or food that is sweet. in my cravings, when i have the acess i will eat several bars or entire bags/ boxes of chocolate. or anything sweet available. when i do not have access to common sweets in the past i have, eaten slices of bread with sugar(white/brown/powdered) on top, or sugar and syrup. eaten sweetened drink mixes.or mixes for making sweet foods, when i didnt have the other ingredients to make the food, i have eaten sweetner packets mixed with chili powder, and at the moment i am eating plain white sugar mixed with syrup. What is causing me to have these cravings for sugar?