My writing on this post is in blue.
http://www.catholicapologetics.org/ap080500.htm
Pope Pius XII, declared infallibly, ex cathedra: "Mary, having completed the course of her earthly life, was assumed body and soul to heavenly glory." (The Magisterium has stayed cospicuously silent regarding whether this process entailed Mary's physical death. The teaching merely states that Mary's body and soul were assumed at the completion of the course of Mary's life.)
Ex catheda, in the Catholic world means that the Pope spoke these words as guided by Spirit and they can never be untrue, infallible (no human on Earth is infallible and that includes the pope. It is not found in the Bible.
Pay close attention to the history defined at this Catholic site below. It appears to have changed over time to suit the time period (God's words are timeless and the same today as they were yesterday, that is Truth). Falling asleep in those days refereed to someone that had died.
http://catholicism.about.com/od/holydaysandholidays/p/Assumption.htm
The verses below are the only accounts that you will find in the Bible, regarding people that went up to Heaven in any other way besides dying a physical death. Jesus ascended into Heaven but He did die a physical death first. There is nothing in the Bible that states that Mary did not die a physical death. She took up her Cross, followed Jesus and died a physical death to be raised again. Again, there is little regarding Mary at all in the Bible. It's just another attempt to distract you from Truth of Jesus and why He came and what we all have available to us through Him. Total Grace, nothing we will or could ever do on our own. Mary was under this Grace as well. She was a humble servant of the Lord and the vessel He chose to bear Jesus. It had nothing to do with Mary and everything to do with our Lord Jesus Christ!
2 KINGS 2:11 And it came to pass, as they still went on, and talked, that, behold, there appeared a chariot of fire, and horses of fire, and parted them both asunder; and Elijah went up by a whirlwind into heaven.
Genesis 5:24
King James Version (KJV)
24 And Enoch walked with God: and he was not; for God took him.
Hebrews 11:5
King James Version (KJV)
5 By faith Enoch was translated that he should not see death; and was not found, because God had translated him: for before his translation he had this testimony, that he pleased God.
Luke 24 (King James Version)--- JESUS
51 And it came to pass, while he blessed them, he was parted from them, and carried up into heaven
John 3:13
King James Version (KJV)
13 And no man hath ascended up to heaven, but he that came down from heaven, even the Son of man which is in heaven.
as·sumed
[uh-soomd] Show IPA
adjective
1.
adopted in order to deceive; fictitious; pretended; feigned: an assumed name; an assumed air ofhumility.
2.
taken for granted; supposed: His assumed innocence proved untrue.
Dictionary.com Unabridged
verb (used with object), as·sumed, as·sum·ing.
1.
to take for granted or without proof: to assume that everyone wants peace. Synonyms: suppose,presuppose; postulate, posit.
2.
to take upon oneself; undertake: to assume an obligation.
3.
to take over the duties or responsibilities of: to assume the office of treasurer.
4.
to take on (a particular character, quality, mode of life, etc.); adopt: He assumed the style of anaggressive go-getter.
5.
to take on; be invested or endowed with: The situation assumed a threatening character.
n.
1. The act of taking to or upon oneself: assumption of an obligation.
2. The act of taking possession or asserting a claim: assumption of command.
3. The act of taking for granted: assumption of a false theory.
4. Something taken for granted or accepted as true without proof; a supposition: a valid assumption.
5. Presumption; arrogance.
6. Logic A minor premise.
7. Assumption
a. Christianity (NOT TRUE , ALL CHRISTIANS DO NOT BELIEVE THIS ONLY CATHOLICS) The taking up of the Virgin Mary into heaven in body and soul after her death.
b. A feast celebrating this event.
c. August 15, the day on which this feast is observed.