A concussion results from a closed-head type of injury and does not include injuries in which there is bleeding under the skull or into the brain.
It is not necessary to keep a person with a concussion awake, although some doctors still prefer to keep patients awake. Some doctors will also order CT scans in order to rule out more serious head injuries. If the person has a minor concussion and they go to sleep it is important to monitor them very closely. If the person cannot be awakened after a concussion, they need immediate medical attention. People who experience a concussion may have a headache and experience some dizziness.
A person does not always get a concussion from hitting their heads. People can also get a concussion by being shaken or from spinning.
A concussion is a mild head injury secondary to blunt force trauma. The brain sustains a mild jarring when the brain tissue comes into contact with the interior of the cranial vault.
All head injury patients should receive a proper physical exam and if warranted a CT (computed tomography, cat scan) of the brain. Whether or not to perform the CT scan is decided by the examining physician. To answer your question I will assume that the person has been examined by a physician and a correct diagnosis has been made. If this is the case, then yes, it is perfectly acceptable to allow the person to go to sleep and actually sleeping will speed recovery time.
Years ago it was accepted that you should keep the patient awake to continuosly assess their neurological status. Present day standards of care reject this theory if serious head injury has been ruled out by a qualified physician.
It is perfectly normal for someone to sleep after they have had a concussion. It is a thing of the past disallowing someone to sleep after a concussion; it is a medical myth. The reason it was done in the past was doctors recommended it to observe the person to see if there were any changes fate the concussion. A lot of people were worried that a person with a concussion who fell asleep would end up in a coma and never wake up. Today we know this isn't true.
One thing to note though is that if the sleep of the person whose had a recent concussion gets progressively deeper and longer, they should see a doctor immediately as it is possible there is internal bleeding in the brain.