My exercise machine of choice for cardio is the eliptical. My 30 min workouts will burn 400cal and my heart rate will rise to 160-170 in about 5 mins and stay there. I have tried doing HIIT on it, however my heart rate then would go up to 200 and only fall to 180 on my normal pace even after 3-5mins at it. Is that dangerously high or should I not be concerned about it?