its not something your going to just develop over night, your body strengthens the heart/cirulatory system, respitory system, even your muscles and basically the weakest one is going to stop you.
Rest up for a few days, then try some long distance runs at a slower than normal pace. If you have a heart rate monitor, you want to be running in the aerobic zone - no higher than 160-165bpm. If you can't go for more than 5 minutes at this pace then there's something wrong and you need some serious downtime.