Concentration when high or low
Being high or low measurably affects how your brain works, which matters for exams, driving and work.
Being high or low does not just feel bad; it measurably affects how well your brain works, which matters for exams, driving, work and any moment you need to think clearly. Knowing that is not an excuse, it is information you can plan around.
- Both highs and lows impair thinking: concentration, memory, reaction time and mood all take a hit.
- A low affects you fast and can be dangerous in the moment, especially driving.
- A high is slower and foggier, and it makes focus and patience harder over a longer stretch.
- This is real and physical, not a lack of effort, and it is worth planning exams, driving and big tasks around.
- Managing the levels themselves is worked out with your team; this page is about the effect on your head.
What a low does to your thinking
Your brain runs on glucose, so when glucose drops, the brain is one of the first things affected. A low impairs concentration, slows reaction time, muddles memory, and makes decisions harder, and it does it quickly. On top of that it commonly brings irritability, anxiety or tearfulness, which is why people who are low can seem difficult or upset for no obvious reason, and why arguing with someone who is low is pointless until they are treated.
The important point is that this happens before, and sometimes without, the obvious physical symptoms, and it can affect your judgement about whether you are even low, which is part of what makes hypoglycaemia dangerous. You are least able to assess the situation exactly when assessing it matters most.
Driving is where this is most serious, and it is not optional advice: a low behind the wheel is a genuine hazard, the DVLA has specific rules about checking glucose before and during driving, and treating a low before you drive is a legal and safety matter rather than a preference. If you drive, that is the one place this stops being about performance and becomes about danger.
The slower fog of a high
Highs affect the brain too, more slowly and less dramatically, but really. Illness, stress and a missed dose can all push glucose up into that territory, and it is the being-high that fogs you rather than the reason for it. A high tends to bring fatigue, difficulty concentrating, slower thinking, headaches, and low mood or irritability, and because it builds over a longer stretch it can quietly drag on a whole day, an exam, or an afternoon at work without you connecting it to your glucose. People often put a foggy, flat, hard-to-focus day down to tiredness when the numbers were the cause.
Sustained highs are more wearing than sharp, because there is no dramatic moment to flag them, just a persistent sense of not being at your best. If you notice your focus, patience or mood reliably dip when you are running high, that is a real effect and worth taking seriously rather than pushing through, because pushing through a fogged brain is exactly what does not work.
Neither of these is about willpower, and that is the message worth internalising. When your glucose is out of range, your brain is genuinely not working as well, and no amount of trying harder fully compensates for the biology. Recognising that changes how you respond: you fix the level, or you plan around it, rather than blaming yourself for underperforming.
Working around it, and what you are entitled to
Because this is predictable, you can plan for it. Around anything that needs your brain, an exam, a test, a presentation, a long drive, aiming to be in range beforehand and checking in advance is sensible, and how to steady your levels for those moments is something to work out with your team rather than improvise. Treating a low fully before starting, rather than half-treating to save time, is worth the ten minutes because a still-recovering brain is a slowed one.
For exams and school, this is where reasonable adjustments come in, and they exist precisely because being high or low affects performance. Keeping your kit and treatment with you, being allowed to check and treat, and having lost time accounted for are standard adjustments, arranged in advance, and covered in full in the exams article. Using them is not an unfair advantage; it is levelling a situation your condition tilts.
At work and day to day, the same logic applies more informally: knowing that a low or a high dulls you means you can hold off on a big decision until you are back in range, and explain to a colleague that you need a few minutes rather than pushing through fogged. None of this is an excuse for anything; it is using accurate information about your own brain to make better choices.
What changes the effect
Speed matters as much as level, since a fast drop hits harder than the same number reached slowly. How long a high has lasted decides how much it wears you down, because it is the duration rather than the peak that fogs a whole day. And whether you are driving changes this from a performance question into a safety one, where the rules are not optional.
How it shows up
Examples, not instructions or doses.
Trying to think through a low mid-paper, with reaction time and memory both slowed. A reason to be in range beforehand and to use adjustments.
A flat, unfocused stretch blamed on tiredness, actually a sustained high. The duration wore the day down, not the peak.
Holding off on something important until back in range. Using accurate information about your own brain rather than pushing through.