As with most problems in life, the issue is never based on a singularity event, but a combination of multiples.
1. Dak's leg injuries have severely affected his throwing mechanics which does significantly impair accuracy. That is why you are seeing a lot of high balls, balls behind receivers, ect...
2. Dak suffered one of the most gruesome injuries you can get on a football field, a dislocated ankle. The man would not be human if he didnt wonder in the back of his mind if he could get hurt bad again.
3. Dak has had a lot of emotional distress, he lost his mom to cancer, his brother killed himself, he was gruesomely injured, his grandmother just died, ect. If he was not suffering through depression right now I would be very surprised.
So you see fellas, its probably a combination of everything. Injuries, mechanics, mental fatigue, depression, ect. If I was big Mike, I would sit Dak down now that the division is a lock, let him get totally healthy and also get him in to see a phycologist to help him get his mind right and to work through his depression. He may need some meds in addition to counseling.