Am familiar with Dex, as a former job required me to be. Much more potent than prednisone, and generally not used unless one is pretty ill. Among corticosteroids, it's the nuclear option. I had a couple clients who developed acne from it, one of its weirder side fx. Trump could be getting it for breathing difficulties, but could also get it for adrenal insufficiency -- JFK suffered from it. Both of the clients I mentioned had to avoid salt and eat potassium rich foods, due to the steroid.
I think actress Kathleen Turner may have been on Dex for a while, which caused a change in facial appearance that was quite stark and impacted her career. A drug to watch out for.
The joy ride was total insanity, and total presidential selfishness, yes. "Hey, they pledge to die for me... guess I'll take them up on that."