It seems like the awakening of the blood magic brought with it a bloodlust that caused the berserk state. I reckon the best way to gather more information would be to speak to the ghosts of the blood mages that remain in this realm, but the text mentions that even they will still drain the blood from the living, so it'd be a risky undertaking.

[She's not a winter power holder to begin with, and she isn't planning on sharing the information with her best friend who is - he's far too adventurous to not look into the matter, and she'd rather not collect him from the flower yard!]

You're right, though... any current practitioners would conceal their activities. Still, from what I hear of the activities of the enemies - the Doctor and his allies -, it doesn't seem to have included blood magic thus far.

[They can't be entirely sure, though, and she'll report these findings to her season's guild leader just in case. After another moment of hesitation, she puts the book in her bag rather than back on the shelf. Her focus briefly drifts to her own ability to change the physiology of her people... it's a power she never used, one of many powers that aren't meant to be used, but isn't it all too similar to this blood magic? Granted, the Founding Titan brings insanity of a different kind.]