Sometimes after running the bases in softball or getting back in the boat after wakeboarding I suddenly feel like I'm going to faint. My heart is beating so fast and yet I'm not breathing fast. I try to take slow deep breaths but it doesn't seem like I'm getting any oxygen, then sometimes my legs and arms will ache and feel very fatigued. It usually takes about 5-15 minutes to go away. Why do I get this? How do I avoid it?