After asking a couple of questions to better understand the weight gain - yes, I concluded that your supposed sugar weight gain, due to being temporary and apparently coincidental with your eating high sodium foods is likely due to increased sodium intake and associated water retention. I'd be interested to know your hydrostatic results before and after these large weight changes (along with error margins of course).
Do you really believe that several ounces of carbs turn to two pounds of fat overnight? And that your metabolism subsequently burns it off over the next day and night (without you noticing a marked increase in your body temperature?)