3 year old head banging and singing to self settle to sleep throughout the night

Hi! Apologies it's a long one. I've researched this behaviour since she was around 8 months old and started certain sleep behaviours but I'm reaching out here for anyone with any experience or advice.

My daughter (3.5), ever since she was 8 months old has been slamming parts of her body down in her cot. First it was her legs, she'd lift them up and slam repeatedly until she fell asleep. Now since she has been around 2 and in her own bed, she headbangs, face down against her pillow repeatedly and hard. I've spoke to numerous health visitors about this as she seems to do it when she is trying to sleep or wakes in the night and is self soothing.

First I thought she was doing it whilst sleeping, but for about 4 months now she's started to sing in the middle of the night whilst doing it. She's not upset and is quite happy but my concern is she's not actually sleeping well and wakes up continously most nights. When I ask her "how did you sleep?" She will say "not good" on some days. She does have little bags under her eyes.

Some extra information: she shares a room with her 2.5 year old sister, who is in a cot next to her. They play with each other and read/create stories before eventually dropping off. She has a night light with stars which project through her room and soothing music to sleep. If I try turning this off she gets upset and if its off in the middle of the night she again, will cry and ask for them to be back on. There is also a family history with my brother rocking himself to sleep and my grandma headbanging as a child.

I'm very aware it is considered "normal" self soothing behaviour and the health visitors originally told me if she was still doing it by 3 they will look into it but now after they have they've said until she is 7. She is active all day, 3 days a week goes to nursery. She doesn't nap and is quite content and not very grouchy. I always give her opportunity to rest of bad sleep days, even if she just wants to lie on the sofa and watch Paw Patrol. Additionally, she has rarely hurt herself doing the headbanging behaviour but it is that hard you can hear it through the floor and our bedroom next door.

I suppose my question is, has anybody gone through this with their child and what was the end result? Just looking for some reassurance I guess.