Hypoxia at altitude is REALLY insidious, and hard to detect until it’s too late
This sounds like a steep, but CONTROLLED descent, that makes me think it was autopilot-initiated..
First Crash-site pic
http://www.ledauphine.com/haute-provence/2015/03/24/un-a320-s-ecrase-dans-la-zone-de-barcelonnette
Seems to be spread out, but there is nothing to give any scale to the pic.