Temper and meltdowns

In the last year J has:

Slammed his door numerous times with such force that the door frame is coming away from the wall! I am considering thre advice of the SENCO to "take the door off"!

Threatened to jump out of the upper window several times and sat on the windowsill, it's winter and the windows are locked but in the summer this is more scary as they are usually wide open.

Damaged his Nintendo 3DS by jumping on it after becoming frustrated by a game (my fault as I was in the bath and didn't realise he had it).

Banged his head during numerous meltdowns and hit himself.

Last week he took a knife from the draw mid meltdown and told me "goodbye Mum" (I got it away from him).

J's school are going to offer support - he is more manageable there with one to one support but less so here at times simply because I struggle to keep on top of everything (crap mother alert).

So I am hoping for a CAMHS referral and help to manage his extremes of behaviour because I feel in the dark when it comes to these meltdowns. Do I ignore them? Do I stay with him? Do I try and cuddle him to reassure which would not be easy?

J's Dad feels that J reacts if I am there but all I can think is that being that out of control during a meltdown must feel terrifying and because of that he NEEDS my presence as a safety net.

All in all I am anxious about his teenage years.