Could simply be frustration associated with giftedness. My DS7 was (and is) like that a lot. It does get better as they start to control more of their world and achieve the things they think they should.
Some things I've learned about my son -- when he's overstimulated (he's an introvert) he needs to be by himself for awhile. It's not a punitive sort of thing (like a timeout), but an acknowledgment that some quiet, alone, playtime is needed to restore equilibrium. Also, watch blood sugar levels. If the swings are happening near meal times, make sure you are giving him frequent healthy snacks.
