What's wrong with my brother?

Over the past few days, he's been displaying odd behaviour, constantly proclaiming that he is "King," and making plans to become President of the United States and bar Barack Obama from the throne.

Yesterday, he sat on a wheelbarrow in public (thankfully, though, there weren't too many people around) and asserted that it is a seat, the President's seat, and then went on to partially disrobe. His overall behaviour became bizarre and fragmented: he ran about and attempted to strip off even more (we had to restrain him, although he escaped); threw off his necklace and watch; and, finally, following an exultant tirade proclaiming his grandeur, leaped to the bonnet of our car and spread his legs (barefoot), saying "I am the president,"laughing uncontrollably and saying, "Emoji people are the most stupid, this foolish meeting." At this point, a show of force was in order and we had to drag him into the car and he's since been involuntarily admitted to a psychiatric hospital (sectioned). He also seems to have been euphoric and full of unrestrained laughter the whole time.

I'm really worried and confused. This is the first time anything like this has happened, and we have no family history of mental illness at all.

What could be wrong with him?