Is caffeine hangovers a thing?

Yes, I know someone who drinks coffee religiously and they will get withdrawal headaches if they don't get that particular number of cups.

Can overwork your adrenals and make you feel fatigued. Caffeine washes out the minerals like potassium, magnesium etc.

Caffeine is one thing but three Lattes with all the sugar and such is another and the real problem you are having I bet.

I drink what my Mr. Coffee maker says is 10 cups in the morning every day, and I have zero issues. It is really only three large cups of coffee and have zero issues every day. It's all the Latte ingredients that got you feeling a bit Blah.

I habitually consume caffeine at work, and none on the weekend.
I find I usually need a day to just sleep and catch up. The lack of caffeine lags me out on the weekend.

Also, make sure you're taking electrolytes. That might help if you're feeling dehydrated/lethargic.

I don't know, but if I drink coffee and don't stay active I crash. I can drink coffee and go straight to sleep 😅

No, just accept that mortals should take about the same amount of caffeine each day.

Dehydration or sugar

You can crash after. I guess you could call that a hangover. I call it the inevitable consequences of tricking your brain into thinking you're not tired when you are, and then you make yourself even more tired until you're ready to collapse.