A concussion is any injury in which there is sudden jarring of the brain. There are some biomechanical forces that occur with a concussion, but the basic idea is that there is a very rapid acceleration and then a deceleration of the brain. According to the Center for Disease Control and Prevention, these may include linear forces as well as rotational forces.
The rotational forces may be injurious to the brain. One misconception about concussion is that you actually have to hit your head to have a concussion. That is actually not true. Any event that jars the brain inside the very small enclosed space with the skull is like a blast. For example, a whiplash injury or a car accident, or anything that jars the brain even indirectly, can cause a concussion. While the majority of traumatic brain injuries are due to accidents-like falls, there is a very large number of sports related concussions estimated per year in the US.
What are the symptoms of concussion? According to WebMD, there is loss of consciousness for less than 30 minutes. That is actually quite rare. Fewer than 10% of concussions are associated with loss of consciousness, but people do develop physical symptoms like headache, dizziness, nausea, sensitivity to light and sound. Cognitive symptoms like confusion, mental fogginess, slowed responses, slurring of speech, trouble with focusing or concentrating losing memory in particular around the event occur as well. A person may have trouble controlling one’s emotions and may also have trouble sleeping. These symptoms occur either immediately after the event or sometimes a few minutes or hours later, sometimes only when people are under stress.