Omega is right. I know that I allowed myself to have a "free" day where I wasn't counting anything on Christmas Day. I stepped on the scale yesterday and I was up almost 6lbs. I drank my 160oz of water plus a little extra, ate very sensibly and got in my exercise. This morning I am not only down those 6lbs. but also an extra one. Now, not everyone can get that number back overnight, I was surprised that I had, but I know that my body is very sensitive to salty foods and water retention, and I usually drink plenty of water regularly so I knew that I could get that out fast.
Panicking only sabotages further progress. If you are still in control of your food choices, then the number on the scale does not matter, because you know that it will come off in time.