You would weigh in lighter assuming you didn't re-hydrate after the workout. What you are doing would be "cutting weight" it's done by alot of professional fighters.
Basically the fighters have to be at a certain weight to fight and they are weighed in the day before the night of the fight. They wear sweat suits and go into saunas on an excercise bike or similar and sweat like mad, then they get weighed in and re-hydrate them selves for the night of the fight. Doing this means they can be as big as possible but in a lighter weight class than their natural weight, people fighting in a 205lb division who weigh 230lb normally for instance.