Normal in 13 month old
I don't know how "normal" it is, but my daughter bangs her head against walls quite vigorously if I allow her. I don't. I intercept and stop her, and tell her "No no no." but in a very soft, soothing voice; I'm trying to teach her that we don't slam our head into things, but I'm not scolding because she's not really doing naughty.
I was told I did the same thing at her age.
This isn't the first time I've heard of this so it isn't an anomoly, but I don't know how common it is or anything else. My understanding is that, when associated with going to sleep or waking, it's a self-soothing thing. He might stop if you soothe him in some other way?
My littlest still does it at almost 18 months, pretty gently and only when really tired. It's seems a bit odd, but who am I to judge?
Unless your kid is doing it constantly, I am sure it's fine and just their way of expressing something.
Mine did this as well, and still does at 2.5. It did scare me at first because my step-daughter (now 14) doesn't know how to deal with ... anything and used to do that REALLY hard even just a year ago. After watching carefully I've found that for mine it's mostly just experimentation. Though I'm wondering if there are other things going on, which is why i'm online today!
I have memories of being little and hitting my head on the wall. I've caught my 12 m/o DD hitting her head on things on purpose, along with hitting her head with her hand and other general silliness. She always has done it like she enjoys the novel-ness of it and I chalk it up to sensorial play/experimentation although DH just thinks she's looney :). I do stop her, say no and redirect her though.