Can moodiness be a reaction to quitting soda?

Today is the fourth day I haven't drunk any soda (soft drinks). Up until a few days ago, all the water I drank was flavored with a small amount of diet Sprite. And several times a week I would drink a few glasses of diet Pepsi. This has been my pattern for several years.

I felt fine during the first three days of not using any soda. And today I feel physically fine (and have no desire to drink soda), but I'm somewhat moody due to an unhelpful thought pattern which has resurfaced. I identified this unhelpful (sorrowful) thought pattern a few years ago as something which resurfaces strongly whenever I would eat sugar. I was able to identify this, because when I don't eat sugar I feel balanced and peaceful. Then, whenever I eat sugar, within a day or so sad thoughts begin to plague me again. Right now my sugar intake is stable, minimal and at the end of a meal.

While I was taking my walk this morning, it dawned on me that maybe the resurgence of this thought pattern could be due to cutting out the soda. Can detoxing from diet soda cause moodiness?

Here's my background: I started the program at the beginning of June 2006, over time got to step 6, and then backed off of step 6, partly because I didn't want to give up the diet sodas. Right now I am solid on steps one through three and on step five (except for two fig cookies after lunch and dinner which are not a brown). I eat very little sugar except for the fig cookies after meals plus a mint or two, also after meals. Other than than, I eat almost no sugar.

I would be appreciative of any thoughts you can offer about any emotional reactions to quitting diet soft drinks.

Thanks,
Grace