sudden aggression question

So, I've had a few hamsters in my life, some Robos, Winter Whites, and Russian Dwarves... and have had mostly great experiences and long-living hammies with no big shifts in behavior aside from cage-mates inevitably getting in scuffles and needing to be separated, but no aggression towards any humans.

So, I've had this current Russian Dwarf, Tina, for exactly one year now (she was pretty young when we got her so she couldn't be much older than 1). She has always been extremely mellow, climbing into anyone's hands without question, never ever once biting anyone, always burrows in her cage, sleeps a lot, and slowly comes out to greet you when you call on her, rarely climbs the bars, generally low-energy compared to a lot of hammies I've known, she usually left a lot of food in her bowl and didn't stash a lot.

However, as of 3 or so days ago, her personality has completely and instantly shifted for the worse and hasn't come back to normal. She's frequently active, day and night, running around her cage, climbing up and falling repeatedly, doesn't leave any food in her bowl, stashes it all in one of her burrows, and worse of all, she is biting like crazy. The second she sniffs your (clean) skin or if you put anything up to the bars of her cage, she will go at it, trying to bite the hell out of whatever it is. If it's your hand, she will break skin. Lightly blowing in her face a little never used to affect her whatsoever, but now a little wind in her face makes her blindly attack and recoil...

I have done enough reading to understand that it's most likely a sign of being in pain, but how would one diagnose what might be the problem? I can't even handle her without getting repeatedly bitten anymore when before I could hold her all day and ruffle her up endlessly and she didn't care. Has anyone had any experience with this type of behavior shift and/or found any distinct solutions? I've heard of constipation, diabetes, or splinters, but I don't really know where to start with her, nothing has changed in her diet/toys/cage/etc. whatsoever... The only thing I changed was her bedding not long ago, but it's the same exact bedding we've always used and she has never once been put-off longer than a few hours after her bedding has been messed with.

I am at a loss, and my mellow, loving, sweet little Tina is now a total unruly little turd. :(

Any info/experiences would be appreciated!