One of Those Moments

There comes a point in writing, for me any way, when three things seem to be happening simultaneously:

1) The words seem to appear on the screen as if by magic and it's as if you're reading what it popping up on the screen instead of writing it.
2) The imagination is fluid and active, of which you are aware of consciously and subconsciously.
3) Everything is coming together to where you "see" and almost experience what is happening and your hands move over the keyboard as if you are playing an instrument.

Is this what composers go through? Hearing the melody and trying very hard to capture it all for merely instruments?