Why did my weight drop suddenly over the course of the day?

When I weighed myself this morning (naked, after going to the washroom), I was 142.  This was the lowest that I had weighed until now.  Then, when I weighed myself this evening, also while naked, I weighed 139.  This was after have having had three meals during the day, and also after having smoked some weed (this is a very rare occurrence, so guys, please don't start moralizing at me.

I've also been visiting a friend for the last two days, so the types of food that I've been eating have been very different than I've been accustomed to.  I haven't been able to measure portions or count calories, I ate burger king hash browns and had dinner at a restaurant yesterday, and I had two restaurant meals today.  I did try to eat sensible portions while eating out, but that's about it.

So, why did my weight drop so suddenly?  Did I somehow shock by body into losing weight because I changed my diet, even though I haven't been able to count calories and I've been eating less healthily than usual?  Does marijuana have some here-to-unknown weightloss property, provided that you don't eat any more than you would while sober?  (I didn't eat anything extra).  Is my scale just broken?  Seriously, I haven't seen the 130s for *years*, so I have a hard time believing it's accurate.

Not to sound gross or anything but did you take a poop right beforehand? Sometimes that will lower your weight. Especially if you are eating different foods and you got blocked up. :)

You peed.  You pooped.  You were somewhere hot and you were sweating.  You were further above sea level.  You exfoliated.  Your body fluctuates naturally about 3lbs either direction, so it doesn't make too much sense to weigh yourself daily or hourly, but weigh regularly and watch for trends over time rather than one weighing to the next. (By "over time" I mean several weeks or even months)

I agree with the others. Your weight may have been a reflection of your actions several days prior (and your "bad" weekend will take a couple days to show up). Once food is in our body, it has to be digested, removed, etc. A lot going on down there.

Fluid, or lack of, can affect weight a lot.

Luckily, I have no knowledge of marijuana or any other illegal drugs.

Congrats on seeing the 130 something marker, every decade down is a triumph. Even if the number was temporary, it will probably be a good motivation.

SUE

Sounds to me that you lost a bunch of water weight.  I'm a competitive martial artist and sometimes before a competition people will cut weight (for weigh in) and they do it by dropping water weight.  It is entirely possible to cut up to 10 pounds in a day if you were ingesting diuretics (green tea, blueberries, kiwi, coffee to name a few) and working out or living in a warmer climate (sweating). 

Drinking more water will cause you to lose water weight too because your body will get rid of the stored water in return for the fresh water so if you found yourself suddenly drinking more water that would make an impact too. 

Natural laxatives can also have an effect; substances like dill weed, yogurt, beans, etc that lubricate your bowels can create a weight drop too.  I would watch your weight over the next couple of days and I wouldn't be surprised if it returned to normal.  I've heard of marijuana relaxing the bowels and this could be part of it for sure.

oooh, ooo!  It was the pot!  Now i know for sure there is a good reason to legalize it! I'll be first in line! Screw Weight watchers, give me mary jane! hehehe