I don't know what sites you're reading but most of that is wrong. Nembutal or any pentobarbital is no longer prescribed for anxiety/insomnia because of how easy it was to die from an overdose. They have been replaced by benzos. Pentobarbital (the name of the chemical in N) is very occasionally used in hospital settings as part of an anesthetic regimen or to treat severe epileptic seizures. No one would dare prescribe pentobarbital to an individual to use at home.
I don't know where you got the info about the overdoses rarely been fatal as there is no antidote for N. If you are found quickly you can be saved but basically undisturbed for 1-2 hours you're going to be dead. Especially at the dose of N in the bottle you get from D.
I guess old and wrong info don't disappear with time or get overwritten so it's easy to get led down the wrong path when searching a new subject. Side effect of the internet age.
OP, read the Nembutal section of the ppeh (peaceful pill e handbook) which is available for download on the front page of the suicide discussion section here on the forums. That's a good starting place. It's not perfect but it's a far cry from the snippets picked up around various sites on the net. Including other suicide/right to die oriented sites. In all fairness there a load of nonsense to be found here on the forums too, interspersed with good info, so we all get tripped up at times. Nobody's infallible.
Most sensible and tactuful people here are reluctant to spell it out for new members. I'd hope and assume, as a precaution to avoid giving info to the wrong people inadvertently. Both from a moral and legal standpoint. Also sources are rare as can be. Right now there's one and it's precarious as hell at the moment.