I m 15 years old, male, 145 lbs and I m not very athlectic (not until baseball season starts at my school, in January or so). When I lay down or even walk/run it seems to return to normal. When I m in a line waiting for something I feel light-headed and I struggle to breath because of my rapid standing heart rate. whats wrong? i don t want to go to a doctor yet because they ll just send me on a wild goose chase.