I do not believe concussions are as prevalent in wrestling as they are in football. Yes, wrestlers do "get their bell rung" especially if both change level and shoot at the same time. I've seen the "mosquito races" a few times from this, but have never had concussion symptoms. The two actual concussions I have had happened in soccer - once getting kicked in the head while going for a head ball and once winning a head ball but taking an elbow or head (hard to say as I never saw it coming) in the process.
I have seen two serious concussions in wrestling: one was when a RH wrestler returned an Irmo wrestler to the mat in an early season tournament in 2011. The Irmo wrestler landed on his head and was out. The other was when wrestlers were doing hall sprints after practice. As they rounded a corner a smaller wrestler pushed a larger kid into the wall.
Concussions are more prevalent in football, imo, as football players are moving at speed over distance. The speed and distance two wrestlers are moving when they shoot at the same time is much less.