Concussions are generally classified on a three-tier scale, with a severe concussion being the worst type. What separates a severe concussion from the other types is that the patient is usually rendered unconscious by the impact. If the person was knocked out for a longer period of time, it is often a sign that the injury was more serious, but any amount of unconsciousness is generally considered good enough to warrant classification as a serious concussion.
Concussions occur when the brain moves too much, causing impacts inside the skull. In a sense, it's like any other type of impact injury, and it takes time to heal in the same way a bruise would. With the brain, an impact injury will generally cause some level of mental dysfunction.
In mild concussions, people usually have trouble thinking for a while and can be easily confused by simple things. There is also often some nausea, and people may have trouble keeping their balance or may even have vision abnormalities. A concussion is considered moderate if the person has trouble remembering what happened during the event, and if the person is knocked unconscious, it is considered severe. A severe concussion will usually have the same symptoms as moderate and minor concussions, but they can be worse.
Concussions can have dangerous consequences if left untreated. In some cases, injuries to the brain can cause swelling or bleeding that can be life-threatening. In general, it is considered prudent to monitor people closely after suffering any type of concussion, and for more serious concussions, people are often placed under medical observation for a while to make sure they don't worsen unexpectedly.
Less severe concussions can sometimes be treated with simple bed rest and avoiding activity for a time. With a severe concussion, doctors generally recommend a certain amount of time in a hospital. There are many cases where a concussion can be accompanied by other injuries, such as a broken skull or some other physical injury that occurred during the impact. Some of these may be more serious than the concussion itself or may increase the chance that the concussion will lead to complications.
There are many common ways that people commonly experience a serious concussion. For example, it is quite common for people to get concussions when playing soccer or boxing or during car accidents. Many sports require people to wear headgear to protect against concussions, but these measures do not necessarily prevent the brain from moving inside the skull, so concussions still occur.