Definition of "realising"

She wakened in sharp panic, bewildered by the grotesquerie of some half-remembered dream in contrast with the harshness of inclement fact, drowsily realising that since she had fallen asleep it had come on to rain smartly out of a shrouded sky.

1914, Louis Joseph Vance, chapter II, in Nobody, New York, N.Y.: George H[enry] Doran Company, published 1915