blue and gold

I workout daily 30 min weight training and 30-45 min cardio. I monitor my heart rate with a Polar HRM. Today, during all my cardio, my heart rate stayed on the high end almost the entire time. It went right back down to normal when I stopped working out but during my workout (which was a very normal workout) I could feel that something was different. I was extremely tired and seemed also to sweat alot more than usual. I cannot think of any thing out of the normal that may attribute to the high numbers. Any thoughts or ideas?