Hello OnionKnight: I don't recall reading, or hearing, anywhere about a specific relationship between concussion & depression in individuals who already struggled with depression. Perhaps there has been some research done with regard to the possibility of such a link. However, my perspective would be, as the saying goes: the proof of the pudding is in the eating. The fact is, from what you wrote, that since the accident you've become extremely depressed. So my thought would be that consultations with both a medical doctor (perhaps a neurologist) & your pdoc or therapist, if you have one or both, would be in order. From my layman's perspective, it seems to me that the important thing here is to address the increased depression you are experiencing, regardless of whether it has been caused by the concussion or is simply a reaction to having been involved in the accident to begin with. The sooner you address this resurgence of depression, the better. As I'm sure you're aware, situational depression left untreated can & does have a way of morphing into clinical depression. My best wishes to you.