Hello and thank you for using HCM. I carefully read your question and i totally understand your concern. But I think you should not wory. I will try to explain you something and give you some tips. It is quite normal during exercise to have high cardiac frequency. For your age we expect that your maximal heart rate might be till 201 beat for minute. Normaly, after exercise we expect your frequency to go down slowly.When your heart beats to fast it is normal to feel a little uncomfortable and even to experience a chest dsicconfort. You are to young to young to thing of other possibility of your chest pain. Sometimes excessive exertion may be the cause of fatigue or this kind of vertigo. If you experience a high cardiac rate during a normal day than we can think of some examinations. If I was your treating doctor I will recommend a blood analyze, electrocardiogram and a echocardiography. It is advisable a holter monitoring to see that really happends with your rhythm. I will advise you to do this simple examination to continue your journey to the marine. Just for reassurance because it may be only a little stress cousin all these. All sow avoid coffee or cofein products because the rise your heart frequency. Hope I was helpful. Wish you good health and good luck in your future