LogFAQs > #980369111

I got that "Hope Preserved" thing to pop up myself and checked through my boons and effects, and nothing seemed to correlate with it. I'm pretty sure it healed me, and my guess is that it happens when you survive several consecutive rooms with very low health, because I had definitely just done so when it triggered.

--Just did a search and it's that Well of Charon item (after the duration, heal X amount). Once it triggers it isn't on your screen anymore so that's why I didn't see anything explaining it.