As far as I know, to terminate hands-free voice dictation mode one must use their hands -- either by clicking 'Done', or by pressing Command + D.
However, pressing Command + D also executes the application shortcut associated with that key combination. (eg, in a web browser you trade your dictation dialog for a bookmark dialog)
How can I end dictation mode using my voice?
Is there an official way to exit dictation without using a mouse?
Is there a way to return to Speech Commands once I've successfully used Speech Commands to start dictation mode? (eg, to get the words 'Computer, open Calendar' to open the calendar like usual instead of merely typing those very words into the document in focus)