My grandmother had a series of minute strokes that were virtually undetectable. Perhaps that is what is going on.
Hi
Welcome to the MedHelp forum!
Yes, it could be a focal stroke, affecting speech and related centers in brain. Then you also need to investigate other causes of brain fog like liver dysfunction (get liver enzymes done—liver function test), kidney dysfunction (get kidney function test done), and anemia. Poor sleep pattern and sleep problems like sleep apnea too can cause brain fog. Sleep studies by sleep specialists can help diagnose this. Low Vit D or Vit B12 too could be the cause.
It can also be a post traumatic stress disorder, if there has been something causing worry recently. Your father needs an urgent neuro-psychatric consult. Take care!