I mean, imo, you got it correct with many of your descriptions:

Fear, Anxiety, Panic, caused by the lack of access to the internet.

Now, I thought I was going to have to coin a term here, but something pretty close already exists:

Nomophobia, fear of not having your your smartphone.

Other proposed terms from other people over the years:

discomgoogolation

abinterretephobia

macriapodiadictuophobia

These have all been proposed as words to mean, basically, fear of not having access to the internet.

Now, you are describing more specifically a fear of an entire, past world without widespread internet access, which is a bit different… as it isn’t just you personally not having your internet device, but the total lack of them, the lack of societal norms built around them, etc.

I would point out that there are still roughly 3 billion of people on Earth, right now, who live without consistent and reliable access to the internet, who cannot afford a smart phone or any kind of internet device.

But yeah, as others have said… before the internet was widespread… we used libraries, we read books and articles and physical newspapers… sometimes, you would have to hunt down a particular rare book, or ask a library to get it loaned from another library, you could wait weeks or months.

I remember an actual physical voicemail machine, an actual physical caller ID device, I remember having to commit my friend’s and family’s 10 digit phone numbers to memory, or carry a small personal contact list with me.

I remember when getting a cordless phone, that would let you go sit down on the couch instead of having to stand or sit within 3 feet of the wall mounted phone… was a completely mind blowing innovation.

And I was born in the tail end of the 80s, before the Berlin Wall fell.

I remember being forced into typing lessons, on an actual keyboard, as one of the very few things my dad forced me into that was actually a good call, and now that the vast majority of younger folks use touchscreens… an increasing number of them have no idea how to actually type, which blows my mind because for the vast majority of my life, not knowing how to type was an extremely stereotypical Boomer attribute.

And now its getting far worse, with an absolute epidemic of students of all manner of subjects who just do not know anything, because they are reliant on some kind of AI to answer all their questions and generate all their answers.

It has been argued before that a human with a smartphone, which they have at all times, is functionally a kind of ‘soft’ cyborg, as the smartphone is a part of so much of their thinking, their culture, their way of life.

So, I suppose its understandable that a ‘soft’ cyborg is terrified by the idea of having part of their brain ripped out, and cannot comprehend how a society could function with everyone not having their portable thinking and communication augmentation.