My leg was behind someone's back while they were sitting on a sofa for around 20 minutes. It wasn't uncomfortable or painful. But after 20 mins I felt like something strange and realised that the part of skin which was in contact with his back has become numb. It's still numb after 6 hours. There's no pain or discomfort or any problems walking. I can feel everything around the area. But just not within that specific area. Anything to be concerned about?