The process of dropping weight causes the body to have to burn up low quality fat that likely has lots of chemicals and other things in it so it is actually taxing on the body to lose weight. Once the weight is lost your heart, lungs, etc. are better off but time should be taken to renourish the body and help the body recover from the effort it spent losing weight. If you do that everything should be noticeably better off than if you were still overweight.