I have been working with in Design for a number of years, producing various books and magazines, using mainly a 'Standard' paragraph style. I sought to introduce a number of slight changes to this recently, mainly to enable some un-indented paragraphs on occasions. When I had tweaked this as required, I tried to save it as 'Paragraph Style 2' which was a redundant style I tried a few years back. I was told I couldn't do this as Paragraph Style 2 already existed, so I then named it as 'Paragraph Style 3' which appeared to save ok. On re-opening the magazine file I found that Paragraph Style 3 had indeed been saved, but the original 'Standard' paragraph had been wiped from the lists, and all the paragraphs done in the original style had now been changed to the new 'Paragraph Style 3' which was certainly not my intention. I closed all the files down, shut the computer off (a nearly new MacBook Pro) and re-booted, but the result was still the same. I then tried to open a file from an earlier magazine, but was told 'Cannot handle the request because a modal dialog or alert is active'. I have no idea what this means, but as the changes have scrambled the text flow in the pages of the current magazine, I have no wish to see this problem afflict all the previous files, which are used now and then for re-prints. Where do I go from here? I have to say this newer Mac has been notably more 'flakey' than any of my older computers!
Hard to say where to begin. If you've been using ID for several years with one paragraph style, you've been avoiding its most powerful capability. It's not really Word or a typewriter; it's a page layout app that is meant to be used in a more complex manner.
So despite your experience, it has to be assumed that you don't fully grasp how to set up a style catalogue. My assumption is that you probably just overwrote your one 'standard' style without realizing that's what you did.
The short form, which you might want to try with a copy of any of your existing docs, is this:
If experimentation shows that things are not happening in good order, or if styles or changes are disappearing, it may be because your doc file is corrupt. This happens in many apps, when a document is edited and saved many times. The primary way to avoid this is to "Save As" to a new file name at the end of any work day, which creates a file purged of all the editing and structural overhead that piles up. The way to fix a file you suspect might be corrupt is:
That both purges the bloated stuff, and rewrites the file at a structural level, with can fix all kinds of little glitches.
I suggest you might find some basic tutorials on ID styles and other major features useful, even if you are using it in the simplest manner.
By the way, you should NEVER use it "Word style," with only one paragraph style and then applying overrides for size, color, spacing etc. That's what styles are for, and their proper use is integral to getting the most out of ID's many features. Sustained use of override formatting makes a doc very difficult to update and edit, and contributes to overall "fragility" that leads to the corruption problems mentioned above.
We can only answer to what's posted. It's hard to read your post as anything but "I only use one style, and trying to use a second style messed everything up."
Using a consistent "house style" has quite a different meaning, but I'm not sure it clears up any part of your issues.
No, there is no reason styles should be lost, overwritten, etc. but there are a number of things that can cause what seems like that behavior, and many trace back to styles management. If you simply haven't created and optimized a lot of styles, there are basic mistakes that could cause some of what you're seeing. It's both a simple process and one that has some little traps here and there.
I really can't tell from either of your posts what might have happened... but it looks a lot like inadvertently overwriting an existing style. There is no solution I can think of but to back up to your last-good version, create any new styles carefully — as in the list I gave, if you have any question about your own understanding of the process — and move forward again.
That you are having cascading layout problems is another thing that proper style definitions (with break, keep and other settings carefully set) help manage and prevent. A long layout should not be a fragile thing, breaking whenever some small change is made; a well-crafted set of styles will adapt to reflow, and need only the occasional touch-up where, say, a head falls at a bad break.
Try starting again from your 'last good' version, and give specific information about any faults you again run into. There's plenty of help here to resolve them.