The best I can tell flash backs can happen with LSD use but only in people prediposed to them because it does produce very strong neurologic activity. But any strong emotional stimulus can cause a real flashback such as combat, physical or psychological abuse.
LSD can also unmask psychological disorders such as schizophrenia. But does not cause them.
The ability to trip decreases over time becuse the neurotransmitters affected by the drug become desensitized. Don't worry though a few days of non-use will allow the potency to return.
No one can overdose on LSD, it doesn't work that way. It attaches to neurotransmitters and once they are used up the rest of the drug is excreted.
I have done up to 10 or so hits at a time and although my perception was scewed (to say the least) I still retained my mental faculties an grip on reality. Some other people I tripped with said they saw ghosts, goblins, angels, etc. but they had a belief in the supernatural. But since my nature is skeptical I saw plants, shadows, or other things that explained (but they did look more interesting) them so it did not bother me much. I did experience odd things but just sat back and enjoyed the experience.
I heard that in Switzeland (I think) LSD is used by psychiatrist to help with treatment. It seems to help with suggestion hypnotherapy because it allows access to parts of the brain or somthing else like that than can dramatically decrease treatment times.
On a personal note LSD, Psilocybin (magic mushrooms), and cannabis can be effective intreating cluster headaches (up to a 96% success rate for psilcybin). I've tried every medicine in the pharmacopia for mine. None work and most have very nasty side effects like addiction, diminished mental capacity, one even lists gangrene as a side effect (the main ingrdient in this drug is ergotamine which, ironically, is what most LSD is made from and is very toxic until made into LSD).
I don't think that the dangers from LSD can be dismissed, but I do think that considering alcohol dimishes so many mental fuctions and is legal we should look at drugs that can actually enhance some mental functions.
If anyone is considering any pschotropic though drug they need to be in good mental condition, most bad trips come from people that are depressed or have other mental problems. This does not apply to cannabis which does not seem to bring about any psychological problems other than a complete loss of memory control.
I know this is off topic but it explains, in a small part, why I don't think anyone should be descriminated against because of past drug use. Our president was a cocaine user and still got the job. This is the same guy that says if I smoke a joint at my house the terrorist win. By the way cocaine deserves its bad reputation.