My hamster Luigi lives free in my room, his cage is open and he can go in there whenever he wants. I bought him 5 months ago and he never had aggressive behaviors until now. In fact, in the past few weeks he started to come on my bed during the night and bite me aggressively on the hands and arms, and it actually hurts! I can't really understand his behavior, even because during the day he's always nice and he comes when I call him. Do you have any idea about why Luigi behaves this way?
P.S I don't really move when I sleep, so there are no possibilities to smash him :)