[a-and]

To add to your anecdote - I also have an extremely high caffeine tolerance and can fall asleep just fine even if I've had an espresso (or two!) after dinner. Similarly to you, I don't really notice the lack, as I rarely drink caffeinated drinks on weekends and have no noticeable dip in energy.

I think your ice cream experience might have an entirely different cause - you were used to stimulation from particular flavors, so when you quit consuming sweet food/drinks. your perception of ice cream was like a bombshell for your tastebuds.

Now, it's entirely possible that artificial sweeteners have detrimental effects on your gut biome or causes a reward response, which create cravings but I'm skeptical until more literature is published on the subject.