Buzzed.

As you may have heard there was a claim recently that Donald Trump drinks up to a 12 pack of Diet Coke a day.  That's a lot of caffeine.  How much?  Online sources, including Coca Cola itself, state Diet Coke contains 46 milligrams of caffeine per 355 millilitres/12 ounces.(Oddly standard Coke and Coke Zero only contain 34 milligrams a can.)  So 12 cans would contain 552 milligrams of caffeine.  Trump supposedly drinks little or no coffee, but that's still a lot of caffeine.

Health Canada suggests the average adult can consume 400 milligrams of caffeine without adverse effects, but suggests not exceeding that limit.  But even that presumably will give most of us a good buzz.  Trump drinks perhaps 150 milligrams more than that.  So there might be a good reason he tweets a lot in the early morning.  The caffeine keeps him awake.