DS6 has been known to have what we refer to as
"grandaddy tantrums". At 6 they have gotten much better but he still has them on occasion. He seems to just overload at times. Like you, I send him to his bed until he can pull it back together. They were really bad from 2-4 yo. Have you looked at anything regarding OE's? (overexcitabilities) I'm told that these amazing tantrums come from being over emotional which it sounds like yours is too. There is a lot of info on the web about it and it's fairly common for GT kids.
Mom to DS 10, DS 11, DS 13
Ability doesn't make us, Choices do!