Part 1 of 2
A lot of people will provide spiritual or philosophical advice. That might help (I have no idea), but it can also introduce a lot of "woo" ideas based on certain ideologies that can make things more confusing. That's because even though the person telling you "ego dissolve blah blah blah" may have some understanding of what "ego dissolve" means to them, that doesn't necessarily help you connect the dots. It can even kind make things more bleak in a way. What the hell did I do? Ego dissolve? Jeesh... it's like you gotta now go spend 3 years learning to meditate, start mantras, and get a PhD in Ego Dissolve Principles, Practices and Mechanics.
Now I'm not against various spiritual ideas and such. If you were Buddhist and understood all that, then sure, it might help for you to connect the dots with Buddhist ideas. But what I'm hearing is that your ideology is pretty firmly rooted in Western ideas, medicine, science, etc.
This reply will take a distinctly Western ideology approach, some of it purposefully tongue-in-cheek. So, "No", the answer is not to pile a bunch of new crap onto you, sending you down a rabbit hole. The answer is to simply help empower you to connect the dots in a way that helps you to feel better about things, cope with your experience, and integrate it into who you are so you can just feel fucking happy again about yourself. Because just like everyone else, you probably have a whole slew of problems that have absolutely nothing to do with this. Finances, health, emotional, and personal health, etc.
First of all, correlation is not causation. You took a drug 9 months ago. You're experiencing some things now. While that drug can certainly shake up your world view a bit, it's not going to be the cause of every little depression or odd feeling. Getting older certainly has it's entire set of existential dilemmas, drugs or not. So just don't be too quick to think any odd little thought, feeling, or depression is because of the LSD. You probably would have come to some of these "realizations" without the LSD. It just would have been a slower, more organic process.
Next, consider that what you took is simply a drug that gave you an experience, kind of like a dream, kind of like hyper-reality, shocking, wonderful, awesome, scary, etc. It forced you to go on a wild imagination trip which your brain considered to be real/surreal/hyper-real. That creates a set of neural paths in your mind that is not unlike any other amazing/scary/intense experience. And since it's a conscious-like state of mind, it's possible to feel/remember that state.
And that last point is important. The thing about different "states of consciousness" is they are separate, kind of like "moods" but more distant, and each state of consciousness has access to certain cognitive abilities, and also non-access to others. That's why dreams are difficult to remember when awake, and "real life" memories are not so easily accessible during dreams. That's why you cannot remember everything about that intense LSD experience, but if you take LSD again, it's likely you'll remember everything again and experience some similar things. So in a way, you now have a "new mood".
It's not necessarily so bad. After you experience this "new mood" multiple times (as you say you are experiencing), you can learn to become more and more "comfortable" with it. You learn that you don't die when it happens. I mean, nothing particularly drastic happens... you don't end up with a broken leg. And it starts integrating with the rest of your life. You've probably adjusted to it a bit already. Think about it. The first time this "new mood" occurred, you probably freaked out big time. After a few more times, yes you might be worried, but it's not as horrifying as that first time. You said so yourself: This sense of dread is cropping up even when I don't have these "flashbacks" as I call them. Why aren't you having "flashbacks" anymore? It might very well be that you're just getting used to the feeling. Now it's bothersome; but not as intense as the first time. What's going on now is you've come to believe that thinking about pink elephants is a horrible thing, and so you try to not think about pink elephants. You can see the futility in this. The anxiety/dread comes from rumination and fear about the whole thing.
Consider why did you take LSD? You wanted to experience something new. Something exciting. There's nothing wrong with that. But perhaps that's something to consider. Perhaps there's something in your life that seemed dull, depressing, unfulfilling, etc. What could that be? Oh about a million of things like unfulfilled dreams, lack of love, wondering what life is about, etc. There's lots of ways to experience new things. Well whatever motivated you to take LSD might "still be there" and need to be addressed. How to address it? I'm not judging anything as right or wrong. Maybe taking LSD is fine, maybe not. Just know that's not the only way to resolve your situation/need/wanderlust/whatever.
It was like the script from a movie about a tragedy, showing how a good person snapped and did evil things. Well this is exactly what you did. You created a movie script. Think about the psychological life that someone like Stephen King (or anyone who writes psychological horror fiction lives. He has a wild imagination, and thinks about things like this all the time. He has to get into each character. Then he writes it down, publishes it, etc. One difference is that his creativity has been developed over a long time, organically, along with his "normal mood/conscious state". So he can navigate seamlessly from one state/mood to another. And the other difference is that while you're paying a psychologist because of this, he's making millions of dollars from his books.
The point is that when you navigate seamlessly from one mood to another, from one state to another, it seems like you have one reality. But you experienced a single, forced, intense (and in this case, creative) burst that was totally separate from anything before. So it created this little "island of cognition" that isn't integrated into your normal state of consciousness.
None of the ideas that you've expressed are particularly "new" or "crazy". The ideas you've expressed are woven into many movie plots, and are metaphors for the modern human condition. I just finished watching "Invasion of the Body Snatchers" (1956) and it has some themes that you've touched on. From http://www.academia.edu/190481/Immanent_Attack_An_Existential_Take_on_the_Invasion_of_the_Body_Snatcher_Films:
And consider the humorous and famous viral video of the guy who called 911 because he and his girlfriend ate marijuana brownies ("Please hurry, I think we're dead"): https://www.youtube.com/watch?v=fNWe3FwpUpE. So yes, even if you're dead and you need help, you can still call 911.
But back to point. This "new mood/ideology/paradigm" is not understood well by your "normal" state of consciousness. It's not a new idea that we've all died and this is some type of afterlife or purgatory. There's about a billion Hindus and many of them believe that what we experience in this life is karma from past lives. And it's certainly a very old idea that the world is an illusion, or that what we think is real is only a filter based on our current belief system. Can anyone say "The Matrix" or Plato's Cave? Think of your experience as a crash course in Western Philosophy 101. Emphasis on "crash". Don't think you have to take LSD to realize all of these things. LSD and such drugs can just force you through it in a quick and personal way.