I do something similar, WYSI- often when I'm waiting for a bus or have to remain in some spot for some time I'll sing or hum a tune in my head (not audibly!) and run the chords with them. There are times when I'm wrong - sometimes, for instance, it will turn out to be a C rather than an Am or a D instead of a D7- but it surprises me how often an ordinary person is able to tell without hearing a sound.

I understand that piano players often lay a banner keyboard in front of them just to practice their fingering. Somewhat the same.