6 y/o has lost his mind on vacation

We are in the UK through January visiting my husband's family. My 6 y/o is not handling it well at all. He's been in the worst mood ever and nothing gets him out of his funk. At first I thought it was jet lag but he adjusted his sleeping fine. I don't think I've seen him smile once yet. Every day he repeatedly asks me when we're going home. I'm trying to stick to his routine as best I can but it's hard in a house with a dozen people.

The house we're staying in is chaotic and it's probably a lot but he's used to big family gatherings at home too. There are four other kids here- cousins 6, 7, 9 and 14, and a rotating crew of them that come in and out too. He refuses to interact with them at all and hides behind me. He has a big family at home who constantly have big gatherings like this so it's not new to him. Last night he was crying because his "hair hurts". Someone touched his head lightly and he had a complete meltdown. I tried to calm him down but he was inconsolable. He cried himself to sleep.

He's crashed out so many times that even my husband's incredibly tolerant family is over it. Earlier he grabbed his aged aunt's phone and tossed it at the wall for absolutely no reason. I immediately put him in his room...so he destroyed it. Pulled out every drawer, dumped out our clothes on the floor and broke anything fragile he could get his hands on. My husband's family is ready to kill me. Tonight he decided to spend the entirety of dinner just repeating "I hate you" to everyone before I gave up and dragged him to bed. My patience is completely worn thin. What is going on with him? We brought both his older sister's to visit when they were his age and they had grouchy moments but absolutely nothing like this. Is this normal? Wtf.