I'm going to break this down for you.
1) The meowing and purring are probably subconscious due to the fact that you bgelieve so strongly that this will work.
2) The craving for milk is also subconscious. You are craving milk due to the fact that you believe cats crave milk, and that isn't the case. Milk from cows is actually known to give cats stomach aches, and really isn't great for them.
3) Humans have a tail bone. This will feel as a bump on the lower back where a tail would be.
So, yes, this is actually in your head. You can't change your DNA. You can't turn into a neko. If people could, don't you think more people would turn into a neko?