I read and report on concussion research as part of my job. One consistent finding in the literature is that, for each concussion sustained, "subsequent concussions occur with less force and take longer to resolve." That's why your 6th concussion (or god forbid, 10th, 11th, 12th...) is more worrisome than the 1st, and why concussion-prone players tend to end up at a point of no return.