I'm no Doc but my understanding is there are degrees of "concussions" (mild, moderate, severe). The diagnosis is made by the symptoms displayed although if the symptoms are severe brain scans, MRIs can be used to see if there is bleeding in the brain. Symptoms can vary from a brief loss of consciousness to an extended period of time, mild headaches to severe, loss of memory for a brief time to a lengthy period of time. The one thing to keep in mind is that any concussion is a traumatic brain injury (TBI).
In college I was concussed after falling off a skateboard and banging my head on a sidewalk. I lost consciousness, and memory for a very brief amount of time-thank goodness because it was during finals week.
