How do you know if you’ve had a concussion?

If you don’t know the signs, it can be a difficult diagnosis. While broken bones can be spotted easily on an X-ray, concussions don’t show up on a brain scan.

Symptoms vary, from head to head.

Some people — but not all — lose consciousness and some don’t even remember getting hit.

Other common signs of a concussion include: vomiting or nausea, feeling dazed, blurry vision, a strong headache, confused thinking, drowsiness.

Immediately after having a concussion, your risk of having a second, worse one increases. That’s why doctors stress it’s important to seek medical attention right away. You should also not return to play sports or other activities until your brain has completely healed.

In the long run, having multiple concussions can affect your mood, sleep and ability to concentrate and problem-solve.

To head off such problems, it helps to have a clear understanding of what a concussion is.

A concussion is essentially a mild traumatic brain injury, said Robert Doss, a neuropsychologist and co-director of the Pediatric Concussion Program at Children’s Hospitals and Clinics of Minnesota.

Normally, the brain sits inside the skull, bathed in cerebral spinal fluid.

When the body or head is struck hard, the force causes the brain to move violently, back and forth, creating a major disturbance inside.

“What happens is the brain twists and turns within the skull,” Doss explained. “The brain cells can get twisted and turned themselves.”

It’s called a neurometabolic crisis.

“These neurons are thrown out of balance,” Doss said. “In response to that, the cells need to work harder to restore that balance.”

This crisis is what causes the headaches, dizziness and other symptoms of a concussed brain.

Finding out what kinds of cellular and chemical changes happen in the brain and how long it takes to restore the brain is the goal of current research.

Sports injuries cause 1.6 million to 3.8 million concussions nationwide each year, according to the Centers for Disease Control and Prevention. But car accidents and falls are, in fact, the leading causes of hospitalization for concussions among kids.

Children’s gets about 2,000 concussion visits a year, Doss said. The average age for a patient is 13.5 years old.

“We know that kids who sustain concussions seem to have greater symptoms and they take longer to recover than adults and young adults,” Doss said, adding that he believes it has to do with the fact that kids’ brains are still developing.

“Within the spectrum of concussion, the vast majority of kids recover within a month,” he said, but “some kids take longer.”