Hmm, hopefully, this can be an important lesson for your "learning curve"!
For images that you want to ensure that you "remember" the processing you have done, you want to at least save the History on. But, more useful is to save a "project file" that has layers intact. And, to take this a step further, if you do an operation on a layer like a filter, give the layer a descriptive name so that at a glance you can tell what you have done. Then, you can check things by turning the layer visibility on and off (clicking the little "eye" icon next to the layer graphic).
Where the history is a must, though, is where you do multiple operations on a single layer, wether the background layer or an image copy layer or whatever. In general, I'd be careful about that to avoid exactly what you are goind through. And, there can only be guesses on a forum like this, and as you've seen, the guesses are that at the best.
One more note. As a "beginner", you may or may not be aware of this, a "related" topic, but it is very important to make sure the original image is preserved. This is done automatically if one is shooting Raw, but in the Photoshop editor you are on your own. Any time you do a Save, you are overwriting the current file (if it has been saved previously). This is a hard lesson that many of us had to learn the "hard way" early on -- once you do that, any "stuff" in the original file is gone. If you do things right, you can regain at least some of the history, but still your original file is dust.
So, one of the first things a lot of us do when opening a file in the PS editor, is "housework" -- doing a Save As either a tiff or a psd to create a "project file" is one of those tasks. And then, having an approach to your workflow that keeps the idea of "non-destructive editing" on-going. What this means in Photoshop is that you don't overwrite your original, and, with the use of layers, you can always revert back to an earlier state -- your Background layer stays intact. Some users may point out that many Photoshop operations are in nature "destructive" and so "non-destructive" is not an appropriate term, and I won't argue, you just have to make your workflow solutions as "non-destructive" as possible.
So, like in the above example: filters applied to an image are by nature "destructive" -- they permanently change the image that they are applied to, and typically in a way that not only can not be undone but that also decreases some of the innate quality of the image. This behavior will depend on what is actually being done, but it is a good assumption to make. So, the only "non-destructive" way of applying a filter is through a layer separate from the background layer -- either a layer created as an "image copy" layer, a layer that allows you to do an operation but keeps separate from the background layer using, say, a white or gray "fill" that you can apply a filter to, doing such thing using masks to hide/show your affects and different adjustment to things like the Blend mode and the layer Opacity, or through the use of Adjustment Layers that are special "lightweight" layers (not image layers) that include layer masks and that with which you can apply an increasing number of effects to your image and which also have Blend modes, opacity, etc.
Yes, filters and such can be fun, and if you use them wisely can be very cool and also save you from making trouble for yourself!
In general, with an important project, you want to Save the project file periodically with the layers intact. The one time that you will go in the opposite direction is where you are preparing the image for final output. This final output will typically be a jpeg in the sRGB color space at a required size and maybe with some "output sharpening". The convenient way of doing this is making sure all your editing steps are completed then saved. Then, you can flatten the file (Layers/Flatten) and do your final operations. You are done with the "serious" work -- having some Actions saved for the Resize, output sharpen and needed conversions (or Save for Web) can speed things along nicely in the end.
One last thing I'll add it that there are times when you can go ahead with doing some stuff and forget about all the "stuff" I've mentioned, and that is if you are dang sure about your techiques and the effects that are being applied. I've seen Photoshop "gurus" give little walkthroughs showing some quick snappy techniques: they open a file out of Lightroom or Camera Raw (note the original Raw file is still intact, and then they just bounce through a few "quick and easy" steps, and then they make an offhand comment like "I'm going to just flatten this right now before I do my next steps" and, pow! The have just done a "destructive edit"!!!
Well, I've wondered about that, especially since newcomers will be looking at that tutorial. I'd personally take a different approach, especially if I wanted to "show my work" to others!
But, I do understand -- if you have expertise in an area and can whip out an editing task in two minutes with your eyes half shut, then at some point it can be simple and efficient to say "done with that", even though a lot of PS teachers will hold the line to all I've said above. I myself would just say "learn all you can" and "master" whatever you can. If you really get some things "down" you can take as many shortcuts as you'd like. For me, as much time as I spent learning Photoshop (and before that Elements) there have only been a few things that I might be so bold at. So, like I mentioned above, some things to put into Actions are very useful. Also, one might have a few tasks one whips through on a few layers and then combining those layers into one merged layer can help you fine tune things and not have your project loaded up with so many layers.
But I will say that that approach doesn't go so far for me simply because I don't have that expertise. Some folks here on POTN are quite advanced and put out some amazing stuff, and then occasionally when one is posting in a way that shows his/her work will show something cool and say "and this took me a couple minutes to do" and I'll think "Wow, that would have taken me a whole lot longer than that
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Well, I'll wrap up my "long...winded" comment here -- help I said something useful!
