Yesterday I Noticed A Quarter Sized Indentation Suddenly On My

Yesterday I noticed a quarter sized indentation suddenly on my left cheek. I disregarded it thinking that perhaps it was the lighting, however tonight I see that it is still there? I'm 35 years old, and I don't get acne anymore, as I did around the age of 20. What else could have suddenly caused this? I have experienced no trama to this area.