is this an actual effect?
No.
I've never heard of HPPD being caused by such a small (threshold!), single time dose of a mild psychedelic. If it were a large dose of a research chemical, maybe. It's like asking if you could be addicted to narcotics after eating a couple of poppy seed bagels.
Most likely what you are experiencing is a combination of two things:
Hallucination by intention: At some level you want to, or expect to see things... and so you do.
or
You are misinterpreting normal visual disturbances as hallucinations. The closed eye visuals you describe don't sound particularly wacky. You might just be daydreaming. In fact some of the symptoms of 'flashbacks' and 'HPPD' occur in normal people. I sometimes see scintillating scotoma, and other features which are characteristic of psychedelic drug abuse. But these symptoms are also normal precursors of migraines, which I have had since I was a kid.
In another example, psychiatry distinguishes between illusions and delusions/hallucinations. For example, if you sit down in your car and suddenly get the feeling that there's a man in the backseat, but you turn around and there's just your jacket and some junk... that's probably an illusion. We all experience illusions from time to time. If you turned around and DID see a man there... then you may have a problem! Sometimes people who have frequent illusions think that there may be something wrong with them, but
usually it's normal - as long as the illusions are brief, don't speak back to you, don't otherwise interrupt your daily life, etc.
I definitely do not recommend that you go out and do psychedelics again, but if you did, you would see that the visual disturbances are not the same as what you are experiencing.
If you said you had an intense vision of yourself in the orange polo, and you bent over backwards and flattened into a desk, then sprouted an arm from your chest which drew a chandelier in space, and then you and everything else shattered into a million multicolored fragments, each of which is either a 'yes' of a 'no,' which flew to opposite ends of the universe, came back together as one, and formed a unity... at which point you finally understood the nature of infinity, and that all the world is binary in nature... and if you experienced ALL of this while awake, in the most vivid detail of any 1,000 page book you've ever read... all in the time it took you to read that enormous sentence... THEN I would say you were trippin' balls!
This is not to say that you don't have a real problem. No one can totally rule out the possibility that there is something
entirely different that is making you feel weird.
You may even have a psychosomatic disorder. If your problems continue you may need to discuss them with your doctor, psychologist, or psychiatrist. I can assure you that if the history you've given us is accurate, that it is very unlikely that you are suffering from a flashback disorder. However it IS possible that you have other problems (psychosomatic, schizophrenic, etc).