I had to sometimes hold my one tantrum child so she wouldn't hurt herself, even though any sense of constriction made her worse. She wasn't a tantrum-for-attention kid, and I never figured out what the cause was. I ended up sitting near her but not touching her (unless I had to protect her) until she was ready ... and then she would not want snuggles or holding: she would shove her head as hard as she could against me and keep tantruming for a long while more.
This could go on for 40 minutes.
It was probably about every other day for about 2 weeks, maybe a month. It certainly seemed never ending at the time.
I had one brother who tantrumed. He lasted more like a year I think. One family friend STILL tells the story of being in the grocery store with my mom, and this brother was screaming and yelling and wailing and thrashing around in the middle of an aisle and Mom was saying very calmly and firmly, "Good job not banging your head on the floor, [name]! Good job!" -- because she had been working with him for quite some time to not bang his head on the floor at home, and she was really truly glad he wasn't banging it on the cement floor and proud of him for achieving that modicum of self-control!
All we can do is take it one day at a time, especially with kids who are reacting to inner confusions and issues.
To interject a note of levity, there was once a funny YouTube video of a kid who only tantrumed if her parents were watching ... if her parents (toting a video camera) moved around a corner, she would hush, pause ... and then appear, looking for them, and as soon as she saw them, flop down and tantrum again ;)! OY! Clearly THAT was all about the reaction ;).