Sometimes I drop two to three kilos in what seems like overnight - using the same scales, not wearing anything. So it's possible but I don't think it's usual.
It generally doesn't happen when I've eaten a lot the day before. It often happens if I've been really active for a couple of days (not necessarily the day before the weight drops off, but the two days before that), or if I've eaten lightly and been active and not realised I had eaten less than usual. That often happens if I've been very busy, too busy to eat as much as usual!
The weight seems to hang around while I'm not eating and then whammo, drop off a couple of days later. It usually comes right back on though, once my metabolism normalises again.
I think a food and activity diary is the only way to work out exactly what is going on.
Failing any logical reason for sudden weight loss I'd be heading to the doctors and insisting on a thyroid check, especially if fatigue or tiredness is creeping in. A friend died at the age of 44 suddenly - she'd been losing weight over a three week period and put it down to the stress of changing jobs and needing to move house. In all other respects she was fit and healthy - her thyroid simply packed up. I don't want to alarm anyone, it's just that sudden unexplained weight loss can be a symptom of any number of illnesses.
With luck you'll keep that weight off and continue to lose weight at a more reasonable rate... that's what I'm aiming for.