in phrase pīti-vegen;’unna “bubbling up with the excitement of joy” overflowing with joy Mhvs.19, Mhvs.29 (expl^d. by uggatacitta i.e. lofty, exalted C.)
■ It may however be better more in keeping with Pāli word-formation as well as with meaning & interpretation to explain the word as ud na, taking ˚na as abs. (base)-form of; nam, thus lit. “bent up”, i.e. raised, high, in meaning of unnata. Cp. the exactly similar formation, use & meaning of ninna ninnata. Thus unna / ninna would correspond to unnata / ninnata.

pp. of ud, unatti & undati, see udaka