How Red Eared Slider turtles can recover from illness?

My red eared slider turtle is sick, I left him out in 8 degree weather and the next morning I found him frozen stiff. I thought he was dead, but my Mom came out and saw him twitch his arms and legs a little so we knew he was still alive. Then the next day I realized that his eyes were closed and red/pink spots were developing on his legs and arms. Recently I've been keeping him indoors by my fireplace, but as of right now his eyes are still closed and he is revealing some listlessness. He hasn't moved, but his head is still out and eyes shut. Please help! I've had my turtle for a while now and I would not want something bad to happen to him.