I can relate, I took a week off and "splurged" quite fantastically in January. When I decided to get back on track, I hopped on the scale, to get a new "start weight". And my weight was DOWN (only by 1 lb, but still down). Of course, then I got back on track, and started drinking my water again, I gained 4lbs back, sat there for 10 days, then finally lost it.
I was not trying to eat sensibly though, I flew off plan, dropped water completely, and did NO exercise for that week. I think I was rebelling about healthy eating in general. I have a different view point now though!