Nearly everyone suffers from a head injury at some point in their life - be it a fall, a sporting injury, or a mishap at home or work.
By Monise Durrani
Producer, Radio 4's Headlong
Every year, over a million people attend hospital with a head injury - most of which are mild.
But, although it sounds innocuous, doctors have realised that mild head injuries can result in long term problems.
When someone suffers a head injury, they are damaging their brain.
Nerve connections can become stretched, disconnecting different parts of the brain.
This can be mild and temporary, or severe and long lasting, and disrupts aspects of mental function, such as memory or information processing.
Most people who suffer a mild head injury do get better quickly.
But some, particularly patients with concussion, who are admitted to hospital, can take longer to recover.
The effects of head injury include nausea, fatigue, intolerance to light and noise, anxiety and depression.
Patients may experience memory problems, or find it hard to concentrate.
And this can lead to difficulties at home and work, thanks to the impact on day to day life.
Headway, the brain injury charity, calls it "the silent epidemic".
Some of the difficulty comes from patients not knowing what to expect.
Ian Swann, a head injury expert at Glasgow Royal Infirmary, said: "Studies have shown that a [concussed] patient's mental function - concentration, attention span - don't return entirely to normal for up to three or four weeks".
Yet patients discharged from A&E rarely receive this information.
Derick Wade, a consultant in neurological rehabilitation in Oxford, said: "The information they get is largely to protect them against having a delayed severe haemorrhage, which is life-threatening.
"It's not information that is trying to help them in relation to the much more likely problems they're going to get from a minor head injury."
And there are people who don't get better even after a few weeks.
In 2001, Gillian Johnstone was a paramedic working in Edinburgh.
She suffered a mild head injury when the ambulance she was in had to perform an emergency stop.
She was expected to make a good recovery, but her symptoms didn't go away.
She explains: "As the weeks went on I started to feel very shaken, anxious, depressed.
"The fatigue was like something I've never experienced before - I was just so exhausted.
"I didn't know what was going on, I just knew I didn't feel right."
She lost her career as a result of the problems which stemmed from the injury to her brain.
For people like Gillian, what is needed is follow-up care: straightforward advice about how to manage their symptoms.
But there is no routine follow-up of head injury in the UK.
Neurosurgeon Sir Graham Teasdale, whose career has been dedicated to head injury care, thinks offering appointments to all mild head injury patients would be impractical, because the vast majority do recover.
He suggests the answer could lie with a very simple method, perhaps based on postal information, with an indication of where to go if further help is needed.
But he is optimistic that doctors are now paying attention to mild head injury.
"It is getting better. The service is not yet there for everyone, but head injury and mild injury is being taken much more seriously."
Headlong will be broadcast on Radio 4 at 21.00BST on Wednesday 12 July or listen online afterwards at Radio 4's Listen again page.