‘F18’ my partner ‘M19’ keeps strangling me as a joke

We have been together for 9 months and the stranglingstarted as play fighting every now and then and not very hard but now it’s an every day occurrence. He does it extremely hard but once I scream or yelp he lets go immediately but doesn’t apologise. And he laughs the whole time as if it is a joke but it’s started leaving marks. I’ve never seen my boyfriend as an aggressive type of person. He’s never raised his voice or his hand to me other than to slap my ass (which he also does extremely hard leaving swelling had prints) but I’ve never seen it as aggression. The strangling is no longer just play fighting even if I’m just annoying him a little bit he puts me in a headlock and puts all the pressure on the front of my throat, so I can’t breathe. The times I get actually scared is when he’s grabs me by the neck and he shakes me back-and-forth but he’s laughing the whole time so I don’t know whether he’s just joking.it genuinely hurts and I tell him this and he says it’s just a joke. And I don’t think, he thinks deeply into it or thinks he’s doing anything wrong. So I don’t know whether it’s actually a problem or I’m over reacting to a joke. Is this just a joke or something more concerning?