Sometimes, when I lift enough to really go out of my comfort zone, I get a rather pleasant feeling afterward which I presume is endorphins and endocannabinoids. One day, I did several sets over time and the feeling stayed for a few hours. I’ve never gotten that kind of feelings while running but that’s likely because I’m not much of a runner.
So, can one get the equivalent of runner’s high by lifting weights? Is it the same physiological phenomenon? Anything interesting to know about it?
Research on it is spotty, with most studies concluding there isn’t a statistically significant increase in endorphins after doing resistance training.
They do note, however, that although this is true for groups, there is considerable variability between individuals, implying that there may indeed be individuals who see endorphin effects from heavy resistance training.
Anecdotally, I am one of these people, and can reliably stimulate an endorphin rush by going over 90% of my max on deadlifts or squats, that endures for a few hours. It sounds like you may be an individual responder also, given the effect you describe.
If so, lucky you! You’ve got a notable advantage in terms of innate motivation to get out there and lift. 
I often miss exercising on my rest days. After a while teaching your dopamine system that exercising is followed by pleasant sensations and reduce stress throughout the day, you get a Pavlovian response and it becomes far less difficult to motivate yourself to exercise. I’ve become increasingly ok with exercising to the point that it hurts, not because I’m insensitive to pain but because I know it’ll be worth it.
I seem to get it pretty easily. For example, standing on 1 leg and raising myself a few inches with the calf muscle. After about 100, I soon get that nice feeling.
I first stumbled upon it when doing jumping jacks in lieu of coffee; Normally, I would have stopped when it got uncomfortable around 40 but I decided: “Fuck it, I’ll do 10 more just to see” and the discomfort did increase but then, it wasn’t so bad. The next time, I did 50-60 and that was painful but then it was over and it felt pretty good.
I’ve noticed that, when pushing yourself physically, there is a sudden steep increase in discomfort at some point. Most people give up at this first phase. If you push past that, it becomes painful. At that point, it seems like it will keep increasing exponentially but if you push past that second phase, the pain levels off then waxes & wanes and then you get a major boost. Having to go through the discomfort and pain is uninviting but gets easier over a period of some weeks.