You've come so far on your journey that a bit of chocolate isn't going to make much difference to your weight but it seems to have had more effect on your self image - tell that negative voice you are the same good person before you ate something, during eating it and afterwards, not devalued at all. ( What?!! I thought everyone heard voices in their head?!!)
I really hope the 5:2 way of eating helps with this (negative thoughts, not the voices) - it has for me and so many others on the forum. Forget about today - even tell yourself it is allowed on a non fast day and go into your next fast day fresh. Do your fasts, don't sweat too much for now and many people find they don't choose the same things on their normal days. CHOICE is the big word here.
Sending you some positivity and support - I know you can do your next fast!!