In fact I really share your opinion and by saying that I was really careful I mean that overdose is really unlikely.
I was using doses, that were more than two times less, than recommended for young plants (though there were no specifications, there was a clear and detailed instruction about fertilizer usage).
I do not really want to counter your words in any way, I just want to find out the real reason. Moreover, problems started before I decided to add more plant food.
Surfed web a lot and still no answer. Many sources relate this problem to a wrong ph, which disrupts proper nutrients absorption.
Growing is not so easy, after all Maybe someone experienced smth. similar?

P.S. Guess I will try to flush the plant with properly ph'ed water. Is it likely to survive? Recover?