While I don't drop 10lbs at once, I do habitually lose nothing - nothing - nothing - nothing - BIG LOSS. So yes, your body can actually kind of store up your weight loss efforts and drop them in one day.
It's kind of like ... you're losing fat constantly, which is dropping your weight, but for some reason you're retaining maybe water. You retain and retain and retain more water each day - hiding the entire fat loss by "weighing something" and masking it. Then one day your body says "we don't need all that excess water" and dumps it - and your real fat loss that was there all along shows up.