It's easy enough to guess. But really, could be intended to mean a number of slightly different things. . Ok, "you" save hime/her - obvious. . "under a rock" can mean obscurity, could mean "in a bad place", can be used to mean "in hidding, hidden" Can mean a general insult, What rock did you crawl out from under? - suggests low-life, undesirable. . So, blind? Likely means "you" saved them from being in a bad place, figuratively. . So for your saying, in your context, give us the context? .

I've never heard of that expression either. We do have a phrase 'you saved my skin' , which means someone has helped you out of a tough situation. Hope that helps

I have literally never heard of this expression before

Some people use the expression "living under a rock" for a person that is not aware of current news and events in the world. If you saved them from "living under a rock", you would tell them what is going on in the world.

For me the term "under a rock" usually is used for two reasons. 1. That a person was in hiding. Like the term "you can't hide under a rock forever" the person was choosing to hide likely due to emotional distress. 2. A person is lacking knowledge or is blind to a situation. Like the saying "have you been living under a rock?" they are surprised the other person had no knowledge about something in particular. Saying that someone saved them from under a rock makes me think this person saved them by taking the time to give them information that ended up being crutial to them.