Hello. Thanks for asking from HCM.
I can understand your concern. The type of 
head injury which needs immediate attention is dangerous head injury. There are few signs, presence of which establish its diagnosis. You should observe for these signs
: vomiting
: 
loss of consciousness more than 5 minutes
: decreasing consciousness
: bleed through nose/ear/throat
: fits
: persistent headache not responding to painkillers
: loss of memory, focal weakness of any limb, speech problem
: altered behaviour
If you observe any of above sign, you must consult ER as soon as possible. The doctor might advise CT head to rule out 
fracture or bleed in brain. Fracture is usually treated by conservative treatment while bleed may require surgical evacuation.
If no above sign, you can observe him at home. My only concern is sound of heartbeat in his left ear. It could be due to bruise on same side which causes increased blood flow in same area and feeling of pulsatile sound in ear. 
Another rare but serious reason could be "traumatic dural artery-venous" fistula. It is establishment of communication between artery and vein resulting into pulsatile sound in ear, 
vertigo, sometimes rupture and bleed in brain. 
It can be ruled out by CT 
angiography of brain vessels. You have to 
consult doctor for it. After confirming diagnosis, it is treated by blocking of communication. 
If his symptom persists and no relief even after applying icepacks, taking painkiller like 
Diclofenac sodium, then you should consult doctor for evaluation.
Hope it will help you.
Thanks.
Take care.
Dr Ishu Bishnoi