I often equate getting into a groove with finding flow during a bout of work. It's an uninterrupted progression toward a goal - where almost everything else in the world is temporarily non-existent.
"I'm getting into the groove" is finding those elusive moments.
On the other hand, 'falling' into the groove could also mean getting trapped. A groove is an interruption in and of itself. And no one wants to find themselves caught in these types of grooves.
So falling into a groove isn't always a good thing.
But as long as you're not in a funk, you won't need to sing the blues for very long. You'll always manage your way out of a groove.