On 16 March 2009, Natasha Jane Richardson, an actress, sustained a head injury when she fell while taking a beginner skiing lesson at the Mont Tremblant Resort in Quebec, Canada about 80 miles (130 km) from Montreal. The injury was followed by a lucid interval, when Richardson seemed to be fine and was able to talk and act normally. Paramedics and an ambulance which initially responded to the accident were told they were not needed and left. Refusing medical attention twice, she returned to her hotel room and about three hours later was taken to a local hospital in Sainte-Agathe-des-Monts after complaining of a headache. She was transferred from there by ambulance to Hôpital du Sacré-Cœur, Montreal, in critical condition and was admitted about seven hours after the fall. The following day she was flown to Lenox Hill Hospital in New York City, where she died on 18 March at the age of 45. An autopsy conducted by the New York City Medical Examiners Office on 19 March revealed the cause of death was an "epidural hematoma due to blunt impact to the head", and her death was ruled an accident.

Doctors said she might have survived had she received immediate treatment. However, nearly four hours elapsed between her lethal fall and her admission to a hospital. Richardson suffered from an epidural hematoma, which causes bleeding between the skull and the brain’s covering. Such bleeding is often caused by a skull fracture, and it can quickly produce a blood clot that puts pressure on the brain. That pressure can force the brain downward, pressing on the brain stem that controls breathing and other vital functions. Patients with such an injury often feel fine immediately after being hurt because symptoms from the bleeding may take time to emerge. This is a very treatable condition if you’re aware of what the problem is and the patient is quickly transferred to a hospital. To prevent coma or death, surgeons frequently cut off part of the skull to give the brain room to swell. Once you have more swelling, it causes more trauma which causes more swelling. It’s a vicious cycle because everything’s inside a closed space.

A CT scan can detect bleeding, bruising or the beginning of swelling in the brain. The challenge is for patients to know whether to seek one. If there’s any question in your mind whatsoever, you get a head CT. Don't ignore the injury just because you feel okay immediately after the injury.

Some of the symptoms of brain injuries: Unconsciousness, inability to remember the cause of the injury or events that occurred Immediately before or up to 24 hours after, confusion and disorientation, difficulty remembering new information, headache, dizziness, blurry vision, nausea and vomiting.

Certain types of traumatic brain injury may increase the risk of developing Alzheimer's or another form of dementia years after the injury takes place.

A concussion may occur when the head hits an object, or a moving object strikes the head. A concussion is a minor or less severe type of brain injury, which may also be also called a traumatic brain injury. A concussion can affect how the brain works for awhile. It may lead to a bad headache, changes in alertness, or loss of consciousness. A concussion can result from a fall, sports activities, or car accidents. A big movement of the brain (called jarring) in any direction can cause a person to lose alertness (become unconscious). How long the person stays unconscious may be a sign of how bad the concussion is. Concussions do not always lead to loss of consciousness. Most people never pass out. They may describe seeing all white, all black, or stars. A person can also have a concussion and not realize it.

The severity of symptoms of brain injury depends on whether the injury is mild, moderate or severe.

Mild traumatic brain injury, also known as a concussion, either doesn't knock you out or knocks you out for 30 minutes or less. Symptoms often appear at the time of the injury or soon after, but sometimes may not develop for days or weeks. Mild traumatic brain injury symptoms are usually temporary and clear up within hours, days or weeks, but they can last months or longer.
Moderate traumatic brain injury causes unconsciousness lasting more than 30 minutes. Symptoms of moderate traumatic brain injury are similar to those of mild traumatic brain injury but more serious and longer-lasting.
Severe traumatic brain injury knocks you out for more than 24 hours. Symptoms of severe traumatic brain injury are also similar to those of mild traumatic brain injury but more serious and longer-lasting.

Get medical help right away if the person: Becomes very sleepy, behaves abnormally, develops a severe headache or stiff neck, has pupils (the dark central part of the eye) of unequal sizes, is unable to move an arm or leg, loses consciousness, even briefly, vomits more than once.

If you or someone you're with experiences an impact to the head and develops any symptoms of traumatic brain injury, seek medical advice even if symptoms seem mild. Call emergency services for anyone who is unconscious for more than a minute or two or who experiences seizures, repeated vomiting or symptoms that seem to worsen as time passes.

And do you know concussions can increase suicide rate several times?

A recent research work has shown that a single concussion to the brain can triple the long term risk of suicides. concussions are now known to be much more serious injuries than once thought. And the danger may not be limited to the immediate repercussions. Researchers have already linked more severe traumatic brain injury to later suicide—particularly in military veterans and professional athletes—and have more recently explored the connection between concussion and depression.

New research published in the Canadian Medical Association Journal shows that even mild concussions sustained in ordinary community settings might be more detrimental than anyone anticipated; the long-term risk of suicide increases threefold in adults if they have experienced even one concussion. That risk increases by a third if the concussion is sustained on a weekend instead of a weekday—suggesting recreational concussions are riskier long-term than those sustained on the job. 

The usual circumstances for acquiring a concussion are not while playing; it is when driving in traffic and getting into a crash, when missing a step and falling down a staircase, when getting overly ambitious about home repairs—the everyday activities of life.

Neuro-scientists  identified nearly a quarter of a million adults in Ontario who were diagnosed with a mild concussion over a timespan of 20 years—severe cases that resulted in hospital admission were excluded from the study—and tracked them for subsequent mortality due to suicide. It turned out that more than 660 suicides occurred among these patients, equivalent to 31 deaths per 100,000 patients annually—three times the population norm. On average, suicide occurred almost six years after the concussion. This risk was found to be independent of demographics or previous psychiatric conditions, and it increased with additional concussions.

Another  study conducted in 2014 found that sustaining a head injury leads to a greater risk of mental illness later in life. 

To protect yourself from serious  head injuries wear a helmet while driving or doing anything that might result in accidents.

( However, let me also tell you a fact: Football helmets don't protect you from concussions. They are used for only to protect against skull fractures.)