I don’t know if it was because his grandparents came and gave him too much attention, too many sweets, or what, but it was impossible. EVERYTHING was a tantrum. If I said no to something, he would cry, scream, throw himself on the floor, and kick as if the world was ending. I tried to calm him down, but nothing worked. I’m exhausted. I don’t know if it was the excitement of seeing his grandparents or if this is a new phase of his personality
I’ve been there. Sometimes it feels like the more love and attention they get, the harder it is for them to regulate afterward. It’s exhausting 
This happened to me exactly when my in-laws visited last month. My 3 year old was out of control the entire weekend and took like three days to get back to normal. Too much excitement, too much stimulation, too many sweets. I think sometimes it’s just overwhelming for them, and they express it with tantrums. It’s not easy, but after a few days, everything calmed down again. Hope it passes quickly for you too.