Merck Manual

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Quick Facts



The Manual's Editorial Staff

Last full review/revision Oct 2019| Content last modified Oct 2019
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What is a concussion?

A concussion is an injury to your brain that temporarily affects your thinking and awareness.

The skull bone protects your brain. Fluid inside your skull also cushions your brain. However, if your head gets hit hard enough, your brain can move inside the skull and bump up against your skull. This may injure your brain and temporarily change the way your brain works.

What causes a concussion?

Concussions are caused by something hitting your head very hard (head injury). This can happen when, for example, you:

  • Fall and hit your head

  • Are in a car or motorcycle crash

  • Get punched in the head or hit on your head with an object

What are the symptoms of a concussion?

If you have a concussion, you may:

  • Be unconscious for a while (usually for less than 15 minutes)

  • Feel dazed, confused, or light-headed

  • Answer questions slowly

  • Have a headache, double vision, or sensitivity to light

  • Be clumsy or have poor balance

  • Have trouble remembering what happened just before or after you got hurt

What is post-concussion syndrome?

Post-concussion syndrome is when you have symptoms after your concussion. You may have:

Usually these symptoms go away in a week or two. Less often, these symptoms last for months.

How can doctors tell if I have a concussion?

Your doctor can tell you've had a concussion based on the symptoms you had after having a head injury.

In order to tell whether you've had any brain injury, doctors will usually:

You may not need a CT scan if your symptoms went away in a few minutes after your head injury.

How do doctors treat a concussion?

Your doctor will have you:

  • Rest

  • Take acetaminophen if you have a headache

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Patients with bulging eyes have eyes that protrude further from their sockets than normal, causing a wide-eyed appearance. With bulging eyes, an individual may seem to be staring or may look surprised or frightened. Which of the following is the cause of most cases of bulging eyes in adults?
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