One of the problems I encountered is, that upgrading to iOS 5 seems to loose iStayHealthy from the apps. I wonder if other people experienced the same problem.
I then reinstalled the app. It seems that all the data I put into the app previously have been saved. So there is no need to put them in again.
Apparently, something must have gone wrong in the upgrade/syncing process.
So - message is: if you can't find the app on your iPhone/iPad after upgrading to iOS 5. simply reinstall the app. Your data should still be there.
And as mentioned in a previous blog: don't forget to set your Notifications in the Device Settings menu - in case you have any alerts (as I do).