My girlfriend won't give me a back massage, how selfish is that?

She claimed she was too tired to since she had been working all night. I was feeling tense and laying in bed and couldn't sleep. I ask for a simple back massage. I sleep in my boxers, so it's not like she had to take my clothes off already, I was already shirtless. She just wanted to sleep. I called her selfish, now she is all mad at me, what should I do?