Willow does this when she wants my attention. She knows that it will wake me out of a sound sleep. Just don't let her ingest the hair, as it is like string and could get caught in her intestine (or at the least, form a really ugly hairball!).
Did you switch shampoos or done anything new to your hair? Once Skinny surprised a friend by licking his hair and it turned out that he used a shampoo with coconut oil or milk. Skinny liked the taste I guess.
I haven't changed hair products recently so I don't think it's that. She only does it when I'm sitting on the couch or if she's perched on my shoulder when I'm sitting at the computer. I really don't like her doing it, so I discourage her at every opportunity. I just wanted to make sure her diet wasn't deficient or something like that.