Hi, The Past Two Times I Have Ridden My Bike,

Hi, the past two times I have ridden my bike, things have gone well until I come upon a steep hill. Halfway up the hill I experience very heavy breathing, almost like I am hyperventilating or wheezing and I have to stop and sometimes sit down. It then goes away but I just feel a bit off the rest of the day. It happened yesterday and today I have a slight ache in my upper back. It was hot and humid both times I experienced this.