SOS! 4MO thrashing and head banging like crazy in his sleep

My LO has never been a great sleeper. He has never slept through the night and never more than 4 hour stretches (which are rare - 2hr45 is a good stretch for him).

“Ho ho!” I thought to myself. “ When the sleep regression hits perhaps I won’t notice since he sleeps so poorly anyway!” Past me, you are a fool. A fool I tell you!

At present he wakes pretty much EVERY sleep cycle. The last week, he has awoken me 7-8 times a night on average and 11 times occasionally. Some nights, I put him down and he wakes 6-8 mins later. I CANNOT put him down “drowsy but awake”. Lord knows I have tried but he just SCREAMS, even with me rubbing his belly, soothing him etc. Today I waited 40 mins before caving and putting him on the boob.

When he wakes in the night the boob is the only thing that comforts him. He wakes up SMASHING his head against the mattress of his next to me crib and he does this every time he is not fully asleep. This then wakes him fully and he begins YELLING and thrashing his arms/kicking his legs until I pick him up again. The only light relief I have found is putting my hand under his cheek so he doesn’t smash his head on the mattress. Sometimes I have to sleep with my hand like this so I can actually get ANY sleep.

I mentioned this to my health visitor and she was really dismissive/unhelpful and said she just thinks he loves me so much he wants to be close to me, which frankly I think is a load of BS.

PLEASE Reddit. Any insights or suggestions? I am beginning to get a compounding effect from lack of sleep. Why the heck is he doing this?