For the past few months, I've been getting these weird almost shiver like feelings across my back and neck. They cause me to tense up and push my head down so my ear almost touches my shoulder. Or it'll just make me push my head back a little and my eyes roll back a bit? This lasts only about a second, and it seems almost voluntary? Like, I could probably not do it if I really focused but it seems wrong to do that and it would make me feel weird for a while. 

Does anyone know if this is related to anxiety, and does anyone else experience this or something like it? I thought I read something about it but I can't find it again.