I feel turned on when i hug my same-sex friend

I'm female. My flatmate is a very close friend, and I am not used to having very close friends in my life. I don't like the idea of kissing her or having sex, so why do I feel aroused sometimes when we hug?

I mean, 'wet down there' aroused, as a bodily function; not 'I want more' aroused.

I like men generally and I sometimes like women, but I really do not feel I would want a physical relationship with this friend.

What is this?? Can other straight-ish women share if they have experienced anything similar with close friends?