iPhone updated itself?!

So I was using my iPhone 4 normally without any problems, then it shuts down out of the blue. This wasn't due to my battery level, which was at 90%. I try to start it back up to no avail. So I plug it into the wall and it says activation required, after the apple logo does this weird animation that I've never seen before (it simultaneously zooms into and fades out the apple logo), so it seems like it's updated its iOS version without my knowledge or consent. I've never seen it say this before. My iPhone is jailbroken (iOS version 5.0.1, tethered, redsn0w, iirc). I've tried to do a tethered boot through redsn0w to no avail; it says jailbreak failed. And it's now in DFU mode and I don't know how to get it back without restoring the thing entirely through iTunes. I really, really do not want to restore and lose all of my data, due to what appears to be iTunes randomly updating itself and demanding I submit to Apple's will. Any ideas?