Thanks for all the replies so far!
First of all, thanks AlmostEasy for the link. My sleep disorders specialist referred me to an opioid addiction center to get it, and I'm not sure I want to do that. I don't actually have a general practitioner for physicals and things and I don't want to get one just for the sake of this one drug. I also don't want to pay $100's to see the alternative medicine folk. I'll give this link some strong consideration.
Beyond that, some random thoughts stemming from some euphoria I'm taking advantage of right now...
I'm pretty sure that naltrexone's action could be described as follows... its an opioid receptor antagonist, which I think is the same thing a re-uptake inhibitor, but for opioids, both natural and unnatural. I think the latter term is more intuitive so I'll use that from now on. That means more endorphins let to roam free in the brain, and the tolerance of pain killers is reduced. Basically, if you take any pain killers, the addictive quality comes about because your brain starts building more re-uptake sites to drain away the drugs faster, which means that you feel more normal when you take an abnormal amount of drug, and feel like crap when you aren't on the drug. The naltrexone binds to these sites, reducing the number of them to a lower amount such that you can take less opioid to feel normal. The brain will also continue to build more re-uptake sites in response to the inhibition of what it has already built, but I get the impression that the rate at which the brain builds more sites is slower in response to a re-uptake inhibitor than it is to more intake of the chemical being re-uptaked.
So, I can certainly see how this drug would work, in the same way that many re-uptake inhibitors work, to maintain your natural endorphin levels in the body. It sounds like the "runner's high" is what you would feel after taking this drug. Again, the brain would start building more re-uptake sites to make up for the excess endorphins, and as such you should technically gain a tolerance to this drug, and feel kinda crappy after coming off of it. Obviously this varies with brain chemistry and genetics. And perhaps this particular drug binds in a special way that the brain THINKS that it has the same number of active re-uptake sites, or shuts off its negative feedback response, whatever, for those folks who are able to maintain on the drug for years.
But I'm pretty sure in my case, I'd build a tolerance in a couple days or weeks seeing as I've seen the same thing with every drug I've taken to improve energy levels in the past.
I went on an incredibly slow 4 to 5mph jog for 30 minutes yesterday for the first time in about two months. Got a subtle runner's high which built through the evening, gave me the most refreshing sleep ever, and I'm still buzzed a whole 24 hours after the jog. I haven't eaten ANYTHING today and I'm still going. This is typical when I start running for the first time in a while. But if I keep jogging every day, the effect wears off until I no longer feel it anymore, just like any other drug I've taken. I've been very much physically fit in the past and maintained it for months, yet felt like crap the whole time! It's hard to describe this... even while feeling like utter crap I could punch out <24 minute 5k's. I'd feel like crap before, during and after. Brain fog. No euphoria. I was doing this to save my life (originally very overweight) and maintain.
It seems that running would be a lot like taking morphine... it stimulates your body to produce more endorphins. Your body builds receptors to drain the endorphin over time... you get tolerant. I wouldn't say I get depressed when I stop running... but this is clouded by the fact that I have just recently had this revelation and was probably doing many things at the time like also drinking coffee, tea, sugar, etc. I need to experiment more with this...
So looking forward, before I try LDN, I think I should start a rotation between stimulant sources like coffee, chocolate, tea and running.
Each of these foods/activities seems to effect the brain in a slightly different way that the brain's negative feedback response needs to address differently, which gives you time to get high on something, stop using it, try something else, and cycle back.
I'll have to run some experiments to collect data points over the next few months. Isolate things and test things without interference.