This is a really hard reply to write.
There could be a few things happening, and it could be a mixture of them, or something else I haven't considered.
Firstly I would ask about your recent breathing tests. If you are experiencing CO2 buildup, it can certainly account for sudden disorientations (like which gear am I in). I applaud you that you realise that driving is no longer safe. Please realise you have had a good warning, it wasn't something that happened whilst you were driving at any speed.
Secondly no PALS can say they are not highly stressed over their diagnosis and progression. I cannot image that any PALS no matter how well they are accepting the disease, no matter how supportive their family or friends, no matter how intelligent, are not experiencing high distress. As a CALS my brain went to mush in many ways, and I'm battling that even worse as a widow now.
Lastly, the statistics show that around 50% of PALS will experience some change in cognition which often shows as a decrease in executive functioning and often language and comprehension issues. When it is a profound degeneration of these functions it is called FTD, but many PALS experience some level problems without being put into the box of saying they have any kind of dementia. This is very different to Alzheimer's.
I have no idea what is the cause there with you, but it could be worth seeing your doctor and have your fears looked at. For example if it is a CO2 issue, it can be addressed with bipap or DPS if you are still eligible.
It must be very scary xx