What Causes Shortness Of Breath?

hi im a bit concern as i recently collapsed today at work. i work at a warehouse . Today i was fine but working in a warehouse it tends to get hot, so i was very hot. I climb the steps to the next level up as the warehouse has two levels. I got up to that level and felt a bit woozy and could feel myself inhaling air faster than normal , as i felt myself short of breathe, i was very hot at the time, could feel my heart rate beating as fast as normal. I realised in seconds my hearing had faded in a short moment of that time. I was gasping for air, i stopped and felt my heart rate getting slower and slower. Before minutes i had collapsed. I come too, within a few seconds after, went to a aircon room and had some water. Took 15mins to come right and returned back to work, still was a little short of breathe, and only worked on the bottom level of the warehouse. before we go any further, i am 44years of age, and a have smoked for over 28years.