Is the ground still soaking wet after ten days? Is the ground boggy to begin with or the plant below grade?

If so then maybe root rot is happening or happened.

Kind of hard to visualize 25 minutes of a hose running would cause root rot in a healthy plant. Our hose ran for 24 hours or more one weekend a couple years ago (we were out of town and the nozzle busted on the hose). Lots of erosion but the Annabelle hydrangea showed no signs of stress from all the water rushing by it. We've had flooding at times (23 inches in a 24 hour period in Sept, 2009) with no ill effect (except some crinum bulbs did not come back the next spring).

Thanks - ground and soil now feel "normal" - certainly not spongy or moist ... no residual water "pool".
Based on your experiences, my having caused root rot does sound unlikely, but I have no other explanation - or evidence: There are no splotches or spots or powdering film on any leaves, and none of the leaves are in any way deformed. They're just all yellowing ...