Ultimately, our lives are in God's hands; even the next breath you take is a gift from Him. If He were to withdraw His hand from you, your life would end (despite the most strenuous efforts of your doctors). The Bible says it well: "When you take away their breath, they die and return to the dust" (Psalm 104:29).
What difference should this make to you? First, it should remind you of your dependence on God. All too often, we assume that our lives are in our own hands (or the hands of our doctors). But they aren't; they are in His hands. The Bible says, "No man has power over the wind to contain it; so no one has power over the day of his death"
(Ecclesiastes 8:8). A brush with death also should remind you that each day is a gift from God -- a gift to be used wisely and joyfully.
But this experience should remind you especially of an even greater truth: This life is not all, and someday you will enter eternity. Your letter suggests that so far in life you haven't given much thought to God. But perhaps one reason He's given you this extra time is so you will turn to Him before it's too late.
Thank God for sparing you -- but most of all, turn to Christ and open your heart and life to Him. Don't let another day go by without Him.