Scale weirdness... How could this possibly be?!

I've noticed something extremely weird about weighing myself. If I wake up, pee, and then weigh myself without clothes, I'll weigh a certain amount - say 145lbs. Then, I usually putter around, drink a bit of lemon water, make some lunches, wait about half an hour. And then I'll weigh 141... I've noticed over the past month that I seem to loose 3-5 pounds in the first half hour of being awake. 

WHAT THE HECK IS GOING ON?! Is there like... gas built up in my tummy or something (doesn't feel like it, fyi!). I just don't understand how this is possible AT ALL. I go by the lower weight (after double checking at the gym) but I'm just SO CURIOUS of why this is.

PS: No eating/BM, anything different between the two weigh ins...  

scales aren't accurate.

If it is digital, I have heard that once a digital scale weighs you it needs like and hour + to re-calibrate according to the manufactures but it could just be and excuse for inaccuracy.

Well, your body does retain a lot of water while you sleep, so even when you urinate first thing in the morning, you're holding onto more water than you would during the rest of the day. I'm not sure if that would account for all of the weight discrepancy, but water does weigh quite a lot (roughly 8lbs per gallon).

That being said, depending on your scale it could be that it's also slightly inaccurate. Remember to keep the scale on a flat, firm surface and step onto it evenly. But pretty much all scales will be inaccurate to some degree. Even the one at your doctor's, if not recalibrated every so often, can weigh you in wrong.

Try to focus on your waistline if you're losing weight, it's results are much more accurate than anything a scale will tell you.

Lemon water is a natural diuretic.  It dehydrates you.

Plus scales have a margin of error too.....

Gravity does change it's strength throughout the day. It's common for your weight to change up to five pounds due to this. That's why people weigh themselves once a week at the same time.