Hi numbfoot

Thank you for your comment.

The orthopedist did the sound fork test only on one foot and did not explain anything before the test. The "test" lasted about 15-20 seconds and after that he gave me his diagnose "You've got peripherial neuropathy":.

It seems that the sound fork used was 128 Hz tool. I just happen to have a 440 Hz sound fork at home. It is for guitar tuning. I made the same test with my own fork and I do feel the trembling everywhere on my feet. 400 Hz is higher that 128. I don't know if my own test any value. 128 Hz sound forks are quite cheap. Maybe I should be one. That might also bring me more stress.