Why is my Nintendo 3DS screen turning off?

My 3DS has this issue where if I leave it closed for a while, regardless of charge, sometimes I will open it and it will remain a black screen. Not off but just black. The blue light is on and the game I am playing doesn't produce any audio. Hoping for a permanent fix as I'm playing Pokemon more recently and would like to not constantly save every time I progress a little bit in the game.