Didn't exercise at all for a week and lost 5lbs. WTF?

So after my big trail run in the hills a week ago I desperately needed some time off of moving at all basically. When I woke up the following day my entire body felt rigid and my muscles, particularly in my legs and back were screaming. I couldn't even walk properly after that 25km hilly race in the woods.

I wasn't going to push it so the only thing I did was to meet up with the people that participated in the race with me for dinner and I was actually quite happy that all of them were pretty stiff as well including the guy that does these sorts of endurance races for "fun."

For the next 2 days the only activity I got was walking around the city to do things that I needed to do like work or get food, but other than that I would do some stretching on a mat in front of the TV, but that was all. I don't think my legs would have cooperated if I had done so much as try to run a 5k.

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I feel as though after exercising pretty damn hard for 6 and a half hours in a row on Sunday entitles me to a few days off though, don't you? I'm pretty sure that sport scientists would recommend that anyway. But just like I remembered in the past, a NEED became a WANT became the starting of a habit. The sorts of habits that resulted in me getting fat all those years ago. After 6 days of sitting down most of the time and also ordering food that I normally wouldn't have - I ate Popeye's Chicken and fish.... TWICE! - I decided to get back into some light exercise and do some cycling. It wasn't tough, after nearly a week I was fully recovered from the run but something surprised me after a week of sitting on the sofa and eating terrible food that I normally wouldn't tough: I stepped on the scale and discovered that I have lost 5lbs in the past week of doing absolutely nothing.

I had been feeling bloated after a week of excess and eating whatever food and even indulging in things that you probably shouldn't ever eat like pizza and fried chicken and chips regularly.

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_{it's a cajun fish chicken and chips combo... it's trashy, but I love it!}

I went from 192 lbs (87.5kg) to 187 lbs (85 kg) in a week of doing zero exercise and eating trash food. I have to say that I am a bit confused about all of this. When I was regularly before the woods race, I was doing an hour of cardio every day, eating protein heavy, low-carb foods for every meal, and being very careful with what I did in every aspect of my life. In the past week, I basically had a "DGAF-I deserve this" attitude towards life in general. I still stayed away from processed sugars but every other aspect of my life was around the same that it was when I got to be a fatty.

This is all very surprising to me because while the race on Sunday did burn a crap-ton of calories, I was consuming around that many calories while I was doing the race in the form of high-carb snack bars for energy. There wasn't much of a caloric deficit on that day and previously, in the weeks leading up to it I had achieved much greater caloric deficits on just a random Tuesday.

So what gives? Anyone have any idea? I mean, I'm happy about this because to me it seems like a free 5 lb loss out of nowhere, but I am just really confused by it all.

I've read about some athletes out there that do a mixup as far as their diet is concerned where they regularly throw in cheat weeks to keep their metabolism guessing. Is that perhaps what this is?