My Fighter Fish is laid in between a small bridge in his tank. Its dark around the tank. no lights are on. He was just laid there not moving. Does that mean he is probably sleeping?

I know this is a generality but when fish that are laying on the bottom or floating on the top that means there either sick or under stress. All of my fish dont lay on the bottom (except the bottom dwellers). I could be off here but If you have a testing kit you should test your water now and find out if that is what might be causing it.

Wait oscars dont sleep...
Because when the fish light isnt on and im not there my oscars usually sit in spots together.
But when i turn on the light or walk near the tank they come up and want food lol.

by fighter fish, do you mean Betta? I think they sleep; or at least rest - in fact, I've read they like a leaf or something soft to rest on. I've only had mine a few days and I have found him resting occasionally on the plant I have in the tank for him.

My O's definitely sleep or rest - I find them laying side by side resting on the bottom - one kinda leans over and the other is usually more upright right next to the other one

here is a bit more info about sleeping oscars.....
www.oscarfishlover.com/sleeping-oscar-fish

They dont sleep as such but go into a resting state but still always alert.