Your body is made up of cells.
Cells need to eat.
Eating helps you function normally & keeps you alive.
You don't eat, your body look for food else where.
Body will trigger 'starvation mode' which means lets store all the good stuff away for the hibernation (FAT!) and start munching on what's there (MUSCLE).
One lb of fat = (generally accepted figure) ~ 3500 cals for one pound of fat.
There is NO WAY you can lose 10 lbs of FAT in 5 days unless you BURN an excess of 7000 cals a day. Even 5 lbs of fat in 5 days would be 3500 cals in a day.
DOUBLE EDGED SWORD HERE, lets say you over exerted yourself and tried this.. your body would most likely go into shock AND triggering your body's 'survival mode' or 'wtf is going on' and AGAIN, store what is needs to survive (i.e top choice would be fat) b/c you are doing something WAY out of 'normal' ...
Thus, in THAT amount of time ANY weight shifting on the scale is mostly water, there is NOTHING else it really can be of value (i.e. significant amount fat loss) which is what you're trying to achieve.
Also, if you pound water during this little trial your body may even hold ONTO what you are drinking (your body LOVES WATER) again b/c it's trying to preserve what it can.
Yes there would be rebound from anything added back in too fast.
Best I can do on short notice without getting out my biology book.