If you get any kind of head injury at all, you should see a doctor right away to check for concussion (physical / neurological examination, possibly CT or MRI).
A concussion results when the brain hits the inside of the skull. This does mean hitting your head can cause a concussion, but you can also have a concussion without hitting the head. This can happen when the body accelerates and then suddenly stops, causing the brain to smack the inside of the skull. Think car accident or any kind of whiplash.
Here's a clear guide to concussions from the Mayo Clinic
The Brain Injury Association has more in-depth information for the layperson about concussion, including some symptoms we might not associate with concussions, such as emotional, psychological, or sleep disturbances.
Patients often come to me after sustaining a concussion. Most see a medical doctor right away, but some try to brush off the injury because they feel or look mostly ok at first, and don’t see a doctor. This is big mistake because some symptoms from a concussion can develop months later, including balance problems, severe depression, even thoughts of suicide. Seeing a doc right away is absolutely necessary to know what kind of injury you have, and that's information providers like myself need in order to treat you safely and effectively.