Life in a Fog

One of the many symptoms of my mystery illness is the "brain fog". It's incredibly frustrating and, I think, the worse part of being sick. It's worse than the pain, the stiffness, and the rashes. All of it combined doesn't hold a candle to the fog.
What is "brain fog"?
The term "brain fog" is often used by those suffering from chronic illness to define a cognitive dysfunction. Wikipedia specifically defines it:

is a term for the "woolly" sensation of a physical obstruction to clear thinking in the brain, often extended to apply in general to neurocognitive symptoms experienced by many people who suffer from neuroimmune diseases such as ME/CFS, fibromyalgia, Lyme disease and multiple sclerosis, amongst others.

It can be symptom manifest of psychiatric disorders such as schizophrenia or bipolar disorder.

The term brain fog is also used often used to describe the relevant symptom or symptoms of inattentive ADHD or resulting from chemotherapy.[1].

Brain fog involves persistent or episodic cognitive dysfunction, and may be associated with forgetfulness, confusion, slowed thinking, distractability, depersonalization, the inability to remember the correct words when speaking or writing (dysphasia or aphasia).

Have you ever been so tired that you couldn't think straight? Or had to wake up suddenly and couldn't immediately get your bearings? That's similar to what it's like having a brain fog. For me there doesn't seem to be any rhyme or reason for the occurrence. Every time it happens it's like my left brain and right brain are refusing to communicate and I'm stuck in the middle.

An example was yesterday (or was it the day before?). I left for a while and, of course, had to unlock the door when I came home. There's 4 or 5 keys on the ring. I honestly couldn't remember which one unlocked the door. I knew that I knew which one it was. But some part of my brain refused to tell me which one. For about 2 minutes I struggled with that. I was glad then that I don't drive.