Whether you had the option to fast or not and made a choice to fast is up for debate. The leading hypothesis point to no: you did not have an option and you did not make a choice.

Some time ago you heard about fasting (you did not invent fasting) and the situation in your life became such that fasting was what you naturally were compelled to do (stress, digestion, you know better than I that you did not simply decide to fast free of any influence). Your "free will" is probably a fairy tale you tell yourself to feel better about your automaton existence.