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Tired vs Fatigue – Cognitive Fatigue, Fatigue Battery, Buffering and Brain Fog

Many of us use the terms' tiredness' and 'fatigue' interchangeably, but did you know they're not quite the same thing? Fatigue is probably one of the most common and probably worst side effects of brain injury. In this blog, we will explore fatigue and how it differs from tiredness. We will also discuss other connected symptoms: buffering, brain fog and fatigue battery. We'll explain what these side effects are and how to recognise if you have them. In our next blog, we will discuss fatigue triggers and ways you can manage them.



What does tiredness look like?

You know that feeling when you've had a long day, didn't get enough sleep, or pushed yourself too hard? That's tiredness. It's a natural response to physical or mental exertion, and it usually goes away with a bit of rest or a good night's sleep. When you are tired, you can usually find yourself experiencing physical symptoms too, like yawning and having heavy eyelids.



What does Fatigue look like?


The day can be going well, and then suddenly, BANG! Fatigue hits from out of nowhere. Fatigue is an overwhelming feeling of exhaustion or lack of energy, which goes beyond just feeling tired. It refers to a state of mental exhaustion where your brain's cognitive functions are compromised, such as:


  • Impaired concentration and finding it hard to complete tasks.
  • Reduced memory capacity.
  • Reduced ability to process information.
  • Difficulty with decision-making and problem-solving.


Other symptoms of fatigue include increased irritability or mood changes and physical symptoms such as muscle weakness, headaches or blurred vision.


"Fatigue is soooo different from being tired. For me, it can kick in at any point and affects my ability to concentrate, my short-term memory and even my emotions." - Mark



So, what's the difference between fatigue and tiredness?

“Before my brain injury, I thought fatigue was just another word for tired. However, I since learnt the difference between that and tiredness.” – Mark


  • Tiredness refers to physical or mental exhaustion that can be relieved by rest. Fatigue is a state of mental exhaustion that affects cognitive function and may not be fully alleviated by rest alone.
  • Having fatigue, you can feel tired or lack energy despite getting enough sleep.
  • Fatigue is more persistent than tiredness. It lasts longer, and it can seriously drag you down both physically and mentally.
  • Fatigue can appear without warning and it can have a more profound impact on your daily life than tiredness.


"I thought I had experienced extreme tiredness until brain injury fatigue hit me! Fatigue hits me in so many ways: It rips out my ability to concentrate or remember a simple conversation. At times, there is no mental ability to process a few simple steps." – Mark


My eyes can glaze over, and I can give you the impression that I'm not listening, in that moment, my brain has had enough." – Mark




Buffering and Brain Fog


When fatigue strikes, it's common to experience what's often referred to as buffering and brain fog.


What is buffering?

When fatigue hits, it can become more challenging to process information, and it can feel like your brain is 'buffering'. Think about when your Wi-Fi is running slow, and your content takes ages to load. It's frustrating, as your technology isn't functioning as you want it to. This is like how fatigue can feel. Your brain is on a go-slow, so it can't function as effectively as it is able to.



What is brain fog?

Brain fog is that frustrating feeling of mental cloudiness and decreased cognitive function. It can be challenging to focus, remember things, or think clearly. It's like your brain is covered in a fog. Strategies such as breaking tasks into smaller, manageable chunks, using reminders or digital tools to assist with memory, and practising cognitive exercises can help combat brain fog.



The Fatigue Battery

A fatigue battery can be described by a great analogy I was given; imagine a mobile phone with lots of apps running in the background. It's great when the battery is fully charged, but what happens when the battery is low? This is exactly how fatigue works. Those apps are the information our brain receives, and we need to be fully charged to deal with them. Fatigue drains the battery like an older, out-of-date mobile phone.




Recognising fatigue


Fatigue can appear without warming, so it is important to understand and recognise when fatigue hits you, so you don't overdo it and crash.


The initial symptoms for me are that I feel my eyes glazing over and sometimes they water a little. There can be a dull ache on the right side of my head, exactly at the point of the impact of my TBI. Yawning is also an obvious one, but I'm sure others notice my blank expression, too. The energy levels drop, confusion kicks in, and sometimes there is the need for sleep. The least favourite of mine is becoming irritable and snappy; that's not my normal style." – Mark


"I can usually tell very quickly when Mark is fatigued, whether it be when he's just got up in the morning or part way through the day. You can see in his eyes that he's not connected to his brain, and things just aren't functioning. His eyes often begin to water too, and he constantly is wiping them. Trying to have a meaningful conversation at this point isn't going to happen. We've just learnt to let it take over and Mark to rest rather than try to push himself, which only exasperates the situation." – Jules




Do you suffer from any of these brain injury side effects?


If you or someone you know experiences any of these side effects, then please seek support and sign up to our webinar. Throughout our webinar programme, we will be discussing different brain injury side effects and ways to manage them. However, if you would like to discuss your symptoms with me, Mark, my wife Jules, or someone else who has been or is going through it, please join our Facebook community and ask away.


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If you'd like to know more about these side effects, learn some coping mechanisms and tools, you can do this via our podcast, webinars and online programmes.