I agree, the knee jerking is embarrassing.
As far as this MD’s note is concerned, I know that on many labels for prescription meds here in the US, it is stated NOT to drive or operate machinery until you are sure you won’t suffer drowsiness or have some other detrimental side effects, (and I assume things are similar in Germany)..so I wonder if Lubitz’s doctor prescribed some medication that MIGHT cause such problems, issued the note recommending he not fly, and Lubitz chose to ignore the note because he thought it would end his career..so he decided to end his career in his own way, meaning to crash the plane..