With the benefit of seven or eight years of hindsight I think I can give an accurate summary of this experience.
It was almost entirely experienced in terms of emotions — depression, wonder, passion, disgust — and imaginative imagery (forgive me if that sounds redundant) which did not feel chosen or even controllable.
In addition there was a thin, intellectual layer, a hardly-articulate questioning of everything I had understood before that point.
It played out over a period of several months.
There was never at any point an audible, visual, or physical component.
(edit: Here's a standard, comprehensive description of what it means to have an 'encounter with God' from a conservative-appropriate protestant Evangelical perspective)