
Symptoms include:

There are a few tips we can keep in mind that can help out with brain fog during the day:
Exercise
You knew I was going to say that right? It is always on the list. But indeed it helps boost our mental clarity. Even just a 20 min walk. In fact, if you are working and you find your concentration is shot try getting up and taking a short walk around, sometimes the act of changing activities to motion and then getting back at it can stimulate the brain.
Eat regularly and snack
Do not skip meals. In fact, have regular snacks between meals. Snacks really help maintain your energy and you will find it helps with mental fatigue.
Change activities or tasks
Sometimes the act of changing what you are doing, shifting the brain from one activity to another can help clear your mind. Then go back to your task and you may find your mind more focused.
Get sleep
This may be difficult if you have insomnia or pain or both, but good quality sleep also helps with combating mental fatigue.
Supplements
I personally use B12 and Rhodiola for mental clarity and fatigue.
Reduce stress
Stress also can be a cause of increasing our brain fog so reducing it is beneficial. One way to help reduce it is with such things as deep breathing exercises and meditation. Even if it is just some short deep breathing exercises during the day to calm yourself down.
Routine is our friend
Established routines help reduce our stress by taking away any stress associated with being flustered or in a rush. It helps maintain balance in the body. It is also beneficial to make lists and reminders to help us remember things, as again this takes stress off of us when we might have issues remembering non-routine events and appointments.
Avoid multitasking
It has been established in studies that the brain actually works better when we focus on one thing… I suspect a lot better for those of us with chronic illness and issues with brain fog. So avoid this inclination of multitasking.
Remember pacing
Take breaks as needed as we can overextend ourselves and small breaks can be greatly beneficial
Do a medication check
There are medications that can cause mental fatigue and if it is an issue that is of concern see if it is a side effect you are dealing with and ask your doctor about it.