“Just because brain fog prevents you doing one thing, that doesn’t mean you have to stop doing everything,” writes Brennan. What that one thing is will depend on your brand of brain fog. Brennan’s book helps pinpoint this by encouraging you to create a profile and keep a record – dare we say a fog log – in order to identify patterns. The overarching principle is to select tasks to suit your abilities at any given time and have a fallback option in the event fog disrupts work.

For example, if you find yourself grinding to a halt on a cognitively demanding project, you might switch to email or other relatively mindless professional admin. Or do some brainless household jobs or exercise (see below) and come back to work only when you’re thinking more clearly. Flexibility – something working from home can facilitate – will “help immensely with feelings of frustration and failure”.

If your brain fog is mild or even moderate, Brennan advocates persevering with the task, based on the rationale of “use it or lose it”. It’s a bit like injuring your leg, she writes. Depending on the severity of the injury, you might be told to keep moving, so it doesn’t become stiff, or you might have to stay off it completely, which will allow it to heal, but at the temporary cost of muscle tone and ability. Eventually you have to start using it again, however difficult and painful.

Keeping a brain fog record can help you analyse the cost-benefit of sticking and twisting. Brennan recommends stockpiling “non-urgent, easy, repetitive, non-taxing or manual tasks” on your to-do list so you can remain productive and still enjoy a sense of achievement. If your brain fog is severe and you can’t switch to a task that doesn’t tax the impaired cognitive domain(s), then recruit reinforcements, ie, ask someone to help.

Severe brain fog in tandem with exhaustion or mental fatigue is a clear sign to stop and go for a walk or rest. Or even nap, as we’re biologically programmed to do in the afternoon – thus improving alertness, learning, memory and processing speed – but societally discouraged from. Which is regrettable, because lack or poor quality of sleep is a major brain fog hazard.

Doing nothing is relaxing for some people; for others, it is anything but. The important thing, says Brennan, is to do something unaffected by brain fog that makes you feel relaxed. And resist the societally programmed compulsion to grind late into the night. Both you and your work will be better for a break that allows the solution to come to you (unconscious thought theory) and restores your attention (er, attention restoration theory).

Finally, don’t catastrophise (easier said than done these days). Remind yourself, as Brennan does, that brain fog too shall pass and has multiple, mostly controllable causes. Brain fog is “simply a signal to take action” and probably not, as sufferers can worry, a sign of cancer or dementia.

Now that you don’t necessarily have to be in the office at 9.00am, there’s more scope than ever to sync professional commitments to your personal ebb and flow (and nap). Wide awake first thing? Befogged by late afternoon? Schedule strategically, diarising your most difficult tasks for when you’re energetic and alert and the least onerous ones for when you’re tired or distracted.

Be realistic about how much you and others can achieve, says Brennan. Not only will unrealistic expectations invite failure and disappointment, but your brain fog will only be compounded by the resulting stress – another substantial contributor that’s also topical. Brennan prescribes reframing stressors as “challenges” and opportunities for growth, seeing yourself as active in, if not master of, your destiny, accepting what you can’t control, looking for silver linings, resisting the impulse to withdraw socially and laughing.

If your job is sedentary, Brennan suggests setting a phone alarm to prompt you to move around every hour or two. Sitting for prolonged periods puts your body into “sleep mode”. And at lunch, get out of the house and your clouded head. Look around.

Aerobic exercise will enable your heart and lungs to pump more oxygen- and nutrient-rich blood to your brain. Regular physical activity protects cognitive function and aerobic exercise, in particular, can restore lost executive function and improve sleep, mood, depression and anxiety, all of which aggravate brain fog. Exercise also ramps up the production of new brain cells or neurons: brain gains, if you will.

Speaking of which, you should exercise your brain, which will grow stronger and even bigger. By learning the layout of 25,000 streets, London taxi drivers pump up their hippocampi (you have two), the areas involved in spatial memory. Learning anything new – information, skills, people and places – can promote neuroplasticity, says Brennan, as can taking existing activities to the next, more challenging level. She does not, however, endorse overhyped, under-proven “brain training” games.

A “fit, healthy, dense, well-connected brain” is the best anti-fog defence, as Sun Tzu didn’t write.