When a person suffers a head injury, the question is, should the patient be evaluated in the emergency department?
The 2014 Head Injury Guidelines [See Ref (1) in Resources] from the National Institute for Health and Care Excellence (NICE), provide excellent guidance on this question. Here are some excerpts (the complete set of recommendations are in the Resources link):
1.1 Pre-hospital assessment, advice and referral to hospital
1.1.1 Public health literature and other non-medical sources of advice (for example, St John Ambulance, police officers) should encourage people who have any concerns following a head injury to themselves or to another person, regardless of the injury severity, to seek immediate medical advice. 
Telephone advice services
1.1.2 Telephone advice services (for example, NHS 111, emergency department helplines) should refer patients who have sustained a head injury to the emergency ambulance services (that is, 999) for emergency transport to the emergency department if they have experienced any of the following:
Unconsciousness or lack of full consciousness (for example, problems keeping eyes open).
Any focal neurological deficit since the injury.
Any suspicion of a skull fracture or penetrating head injury.
Any seizure (‘convulsion’ or ‘fit’) since the injury.
A high-energy head injury.
The injured person or their carer is incapable of transporting the injured person safely to the hospital emergency department without the use of ambulance services (providing any other risk factor indicating emergency department referral is present; see recommendation 1.1.3). [2003, amended 2007 and 2014]
1.1.3 Telephone advice services (for example, NHS 111 or emergency department helplines) should refer patients who have sustained a head injury to a hospital emergency department if they have any of the following risk factors:
Any loss of consciousness (‘knocked out’) as a result of the injury, from which the person has now recovered.
Amnesia for events before or after the injury (‘problems with memory’).
Persistent headache since the injury.
Any vomiting episodes since the injury.
Any previous brain surgery.
Any history of bleeding or clotting disorders.
Current anticoagulant therapy such as warfarin.
Current drug or alcohol intoxication.
There are any safeguarding concerns (for example, possible non-accidental injury or a vulnerable person is affected).
Irritability or altered behaviour (‘easily distracted’, ‘not themselves’, ‘no concentration’, ‘no interest in things around them’), particularly in infants and children aged under 5 years.
Continuing concern by helpline staff about the diagnosis. [2003, amended 2014]