Ran longer than usual, heart pounding, short of breath when I was resting. Do I do more or less next time?

Exhaustion. If you were uncomfortable and felt unwell after running, then clearly you should run less next time. It is normal to have fatigue and heavy panting after a hard run, but it should not make you actually feel sick. If you're feeling sick, something is wrong, and you should change your work-out routine.