i wake-up from sleeping at the early hours of sleeping at night as if am been disturbed or feel that my heart will stop but if i gone into sleeping after this, this doesn't happen, bear in mind that i excercise every singlt night for two hours - both with heavy weights and cardio excercises, am 35 years old, no cholestrol at, have no fats, have pretty good muscles and 6 packs as well, why is this happening?