I think it's safe to say this is enough proof to show that I could have gotten a concussion from a slap to the head, based on this info across numerous sites: (The number of concussions you’ve had. Because the brain is more vulnerable to injury after sustaining a concussion, it may take significantly less force to cause a future concussion. Also, future concussions may result in more severe and longer-lasting symptoms)
How Many Concussions Are Too Many?