Help! Explosive 9 year old

[OneWildCat]

Hi all,
I hope someone can help. Our 9 year old has always had the off behaviour incident at school. In the last 5 months these have got more regular.
Hes also become explosive at home.
to the point where he goes from 0-100 in a matter of seconds. His gut reaction in most situations is anger and he’s become horrible to his little sister.
We are exhausted and treading on egg shells trying not to say the wrong thing so we don’t trigger him. It feels very controlled.
we had our first appointment with a private child psychologist yesterday and we need to observe his different states and triggers.
I just don’t know what to do. He’s taking over our lives in a really negative way and I don’t know how to make it better. When he has an outburst he throws things at me. Anyone been through similar?

What is his behaviour like the rest of time at school/home? Does it literally come out of nowhere when he is angry or is there a buildup? Does he have any SEN/neurodiversity that have been noticed by school?

He can be quite hyper but can also be so thoughtful and loving. At school in general is ok but the quality of his school work has dipped and he is opting out (although I am convinced he’s copying a friend he’s seen doing this).
behaviour at home is getting increasingly manipulative