"somewhat depressed," 1706, from hip (n.) "melancholy," variant of hyp, short for hypochondria.
Online Etymology Dictionary, © 2010 Douglas Harper
Examples from the Web for hippish
And she might be hippish and drooping for a longer time, and be no less easily at last cured.Six Discourses on the Miracles of our Saviour
I want something of another cast; something that will urge me when I am hippish, without keeping me in order when I am whimsical.The Wanderer (Volume 3 of 5)