A concussion you get through a bump or hit against head or skull. Unconsciousness, nausea and vomiting may follow. (Temporary) loose of memory is possible.
A few days rest, exclude stimuli (light, sound).

Our brain has around 1 billion neurons, with 1,000 connections each, accounting for 2.5 petabytes (million megabytes) of storage. This corresponds to 3 million hours on a DVD recorder, good for 300 permanent viewing pleasure. One mm³ cerebral cortex can contains 2000 terabytes of info, sufficient for storing all films and trailers that were ever made (I read at the end of 1920).

Even when you rest, your brain turns off more information in 30 seconds than the Hubble space telescope processed in 30 years.

In 2015, a Brazilian neuroscientist calculated that the number of 100 billion nerve cells assumed until then would be in fact around 86 billion neurons.

Our eyes send 100 billion signals per second to the brain, which it has to supplement and reconstruct approximately 90% for e.g. face recognition etc.

(The statement that we only use 10% of our brains is not reflected in any scientific research, it is not true.) Teen brain is about 80% complete. The synapses are only fully developed from 25 years (or a little later).