Suddenly better fitness with weight loss!

So, I don't live near a gym, but in December I started biking several miles, including a long hill, three days a week (when it wasn't raining). For the first 6 weeks, I always had to stop and rest several times. Then all of a sudden this week, I just powered up the hill without stopping. I wasn't even out of breath. It was amazing: like I had jumped overnight to a whole different fitness level. I've lost 18 of the 25 lbs that I need to lose, so maybe my body is just more efficient because it's hauling less weight around. But it's an amazing feeling, and I'm so happy!!