Injury severity is determined by factors like loss of memories, amnesia, and loss of balance. Your head injury is mild if you have symptoms that last less than 15 minutes and do not lose consciousness. Again, if the symptoms last for more than 15 minutes and there is no loss of consciousness, it is also called a mild injury. Well, once you lose consciousness, sometimes for just a few seconds, along with other concussion symptoms, you can assume you have got a severe injury. Never take any medicine without the doctor's advice. Finally, do not go back to work until you have fully recovered. Only go if your doctor allows you.