Excellent observation! Most seizures do occur during the night, more specifically, while asleep. https://www.healthline.com/health/epilepsy/nocturnal-seizures This lends more weight to this being a form of wry neck.
Give her all of the vitamins I suggested for the next two weeks for certain, including that calcium plus magnesium. Continue to monitor her at night with the camera.
That the seizures only happen at night may contain a clue to what's causing them. Perhaps she's ingesting enough of these...
That was frightening to see. I would guess she has something neurological going on. It would be hard enough trying to diagnose in a human let alone a chicken. But some seizures in poultry are caused by vitamin deficiencies, so that's definitely something you can do something about.
I would...
I had a rooster many years ago that had occasional seizures while on his perch. Once it happened in front of me. I gave him a baby aspirin each day for a few months, and it seemed he wasn't having any more seizures. But a few months after I stopped giving him the daily aspirin, I found him dead...
Those vitamins are a good idea.
I was thinking if it's not an ear infection, perhaps she has a tumor pressing on her brain. Feel her head to see that it's symmetrical. On the off chance she has an inflammation in her head causing this, try giving her one-quarter of an ibuprofen in the evening...
People believe chickens hide pain, but they almost always let you know when they hurt and where. If the head or ears or eyes hurt, they scratch their heads. If their feet hurt, they peck at their feet. If they hurt in their gut, they stand with their tail down low and flat.
Look into her ears...
This is a tough one. You've ruled out all the obvious stuff. So we're left with the rare causes. She may have a cardio-pulmonary genetic issue causing seizures at night. About the only way to verify that would be a camera going all night to record it if she seizes up, flaps her wings madly, then...
The reasons why a chicken falls off the perch at night can be many, from very simple to complex.
First, the simple issue of untrimmed toe nails can prevent a chicken from being able to curl its toes around the perch and triggering the "lock" position can be responsible. Check her nails and trim...