It's normal to fluctuate wildly on the scale from hour to hour even. I typically weigh 5-7lbs more at night then I do in the morning, that's a lot! It's also attributed to food I have had and all the water I drank that day. Don't sweat it and try to resist the urge to weigh yourself more then once a day.

If I have really gone crazy the night before and I feel heavy when I wake up, I will skip the scale all together and continue on my plan like nothing happened. The extra "weight" will drop off in a couple days.

Agree with everything posted!

One more possibility for you - there could be a food or chemical in that meal you had that you have a sensitivity or allergy for. There are two artificial colors that I need to watch out for, because either one can cause me to add 3-4 pounds of water in just a couple of hours. I can literally watch my hands swell up. Like everything else, though - it flushes out in a few days once I resume my normal clean diet.

Weighing at night just isn't wise - your weight is far too affected by your water and nutrient consumption to get a decent picture of what your mass actually is in any significant way. If you can manage it at all, please weigh when you haven't had food or drink for at least six hours. Weighing less in the morning is why it is more accurate - less food and water fluctuations mean a more consistent weight trend, day to day.