I Had A Fasting Glucose Test Done At The Hospital.

I had a fasting glucose test done at the hospital. by before level was 7.2 and after the glucose drink at the 2 hour mark my level was 4.1. My question is why for the next 4 days after this test did I drop 9.5 lbs without changing anything in my diet. now 3 weeks later I have gained 5.5 of that back.