I can go to bed at 225 and wake up 6 hours later at 223.5. I don't know if it's my scale or I just managed to lose 1.5 lbs in my sleep. Either or it happens all the time. I normally can go to bed Sun night and know if I'm going to have a good weigh in or not. I only count Mon as my weekly weigh in. Like the day I lost 6 lbs during the run, I found 4 of that with liquids and lunch. I've been up 6 lbs before during the week to end up losing 2 come Mon. If you can hack it, I highly suggest to get on the scale more often (AM pref) so you can understand how your body works. I'm sure everyone is different but you don't know till you try.
Moral of the story, don't be freaked out if your up 2-3 lbs. One trip to the bathroom could sort that right out. :)