God I love to sweat!

I've been exercising at the gym for about 3 months now. I was on the treadmill and have been going at a pace of 4.0 miles an hour. One of the trainers said "you seem to be pretty comfortable at that speed. Why don't you increase a little bit so I did to 4.4 miles an hour." It felt comfortable cardio wise. I was able to talk with ease still my little legs had a hard time keeping up and then he said "why don't you try running"?? I haven't really ran since last november when I got so short of breath I just said "forget it". I started jogging, it was okay so I ended up increasing til it felt more comfortable at 4.8 miles an hour. I did this for about 15 minutes before I felt I needed to stop. I haven't ran like this in over 25 years. When I was done with the running/walking on the treadmill after 40 min I was soaked(hair was dripping). God I love to sweat!!!!