Of all our “a-” words, our very last is one of the mysteries.  The “a-” is not likely to be the intensifier preposition 1, but its true root is hard to disentangle from the distinct verb “awaken” or the obscure word of parallel meaning, “awecche.”

• 07.108 It was full morning when he awoke.
• 08.065 and when he was awake he was not pleased at all.
• 14.041 for they thought that war was awakening again,

“awake, v.” OED Online. Oxford University Press, March 2015. Web. 18 May 2015.

“† aˈwecche, v.” OED Online. Oxford University Press, March 2015. Web. 18 May 2015.