I don't normally drink a gallon of water... but I did drink 4 glasses of water within an hour before I began.
And since you were a bit more polite about my excercise habits this time... the reason I do such short cardio sessions is because my lung capacity is decreased due to chemical pneumonia and a while back a physical therapist said to keep cardio workouts short because with my lung capacity as low as it is, I actually can't supply my body with enough oxygen for longer workouts until I'm in VERY good physical shape... and I'm not even close =) When I was seeing the physical therapist, she had me riding a bike for 3 minutes, then stretching (knee injury) and doing some strength training for 2 minutes. But I don't have all that same equipment anymore so I pretty much just work with what I have.
*EDIT* To give you an idea of how my physical condition, combined with decreased lung capacity effects me, I get winded just walking. Back in 7th or 8th grade I could run a mile in less than six and a half minutes easily... I probably couldn't run a mile in less than 10 minutes now.