Do facial muscles weaken over time if they are used less often, like other muscles of the body?

Before I had my last long term bout of depression, I always had a big, bright, wide smile. I have noticed, recently, that my smile now seems tighter and smaller. I can even feel a tightness or stiffness in my face when I try to smile. I mean my natural smile, not forced smiles for photos (though it is noticeable there, as well.)
I am not the only one who has noticed, people who know me well can also see the difference.
Is it possible that going for a long time without happiness (presumably I was doing less smiling), that my smile muscles are weak? Or is this just likely something about the way my face is changing as I get older?

So now I am really just curious, do facial muscles work that way?