I know the feeling....for me I think it is almost a release for anxiety, a kind of hypomanic state in which I feel fine while I am yammering on but when it stops....
even worse when someone points it out. It does take on a life of its own when it happens.

In reaction, I become more quiet, withdrawn, and maybe being too alone contributes to this. (when I was young and hanging out with friends i don't recall this happening...and for years in my early adulthood....)