My resting heart rate is 120 bpm. I'm 16 years old and 152 lbs. And I'm in good shape. My heart rate has been like this for a few weeks. It didnt effect me til recently. I got out of the pool after a swim race (100m freestyle) which is a relatively easy race, then i suddenly felt excessively lightheaded and weak. Light became slightly overexposed and i felt as if i was going to pass out. Then my heart rate stayed extremely high (same as the moment i got out of the pool) for about and hour then it slowly came down. I tried drinking lots of water but it actually made things a bit worse. It felt like my brain wasn't getting enough oxygen and it was hard to breath. any ideas of whats going on?