I doubt that the few minutes you might experience from a night terror/mare would harm you at all... remember the stress tests, the step tests... it raises your heart rate to pounding, but the key is how quickly the heart resumes it's normal rhythm, rate etc? Within 3 minutes is excellent!

Sometimes when we have aggitated dreaming, it's like we're running a marathon... the best thing is to get into the best shape you can... and not worry about it TC!