Don't do this if you are reading this. Reinstalling it didn't work for me and others. I think we are all waiting for some sort of fix! HELP Samsung!
I was having the same problem with sensor on phone not working. I uninstalled/reinstalled the HEALTH app and now find there is NO WAY to "measure" heart rate/stress level anymore (no prompt on phone app). The info is taken directly from the Galaxy Fit which I don't find as accurate as a finger pulse on the phone! So no more sensor??? Also lost all 3200 steps this morning with the install.