I have a cat that does the same for me. She just seems to know when I need some comfort. Of course, she uses ME as well, LOL! She didn't used to sleep with me, but she has begun to do that. I work nights and sometimes take a nap mid-afternoon if I didn't sleep well the night before. That's when she comes and snuggles right in the small of my back. It helps me sleep better, I think. I can feel her purring vibrating in my back.
She is the best kitty. She's very playful, but also very affectionate. I have been grateful many, many times for her.
Kay