I get out of breath and my heart starts? Beating fast for absolutely no reason and then stops. What could this be?

May be serious. There are many things that could be going on that cause the sense that your heart is beating fast at times. Most commonly, it is a "premature beat" that feels like a flutter and is harmless. However, it can be other dangerous heart rhythms too, so this is something I would definitely get checked out as soon as possible.