What I find intersting is the idea that happiness might be enhanced through the use of these techniques.
I'm no scientist but I think I can shed some light on this issue.
I am always wary of things like this, because the situation isn't static. A good example is the stock market. Imagine someone who owns a bunch of stock decides that he or she thinks their stock will devalue, so they sell their stock. Then some other people see them sell and they think that person must know something, so they sell. This chain continues until many people have sold stock and the stock devalues. So did the person sell because the stock would devalue, or did the stock devalue because the person sold?
As you can see, this works both ways. Perhaps you convince yourself that happiness is a skill, or at least you suspend your disbelief and decide to give it a try. So you take more breaks, reward yourself on occasion, etc, and you become more happy. So was there any skill involved? No, of course not. You changed your routine and that made it better.
I just think that often once the ball is rolling, it picks up speed. I don't believe this mumbo-jumbo about meditating and whatever. I think it is self-reinforcing. The person meditates, they feel a bit better probably because their routine has changed and that always feels good, they attribute it to the meditation and continue down that road.
Similarly, a smoker comes to relish the calming effect of cigarettes but of course cigarettes have no calming effect, that effect is sating the body's craving for nicotine. If one wants to be calm, one should cut out cigarettes altogether.
So I see in all these things a tendency to mistake the nature of the effects concerned. I don't see that one can choose to be happy but I see people trying to be happy like the smoker trying to be calm; their habits must change. If one identifies those habits that lead to one feeling unhappy then I think one can evolve to become more happy generally.
I don't know about others but my own experience was that when I was on holiday or something like that, the worst time for me was always the last day. If it was the weekend, it was Sunday night. If I was away, it was the day I was returning home. It always felt terrible, like that happy period I had just experienced was gone forever. I suppose it is like the smoker who reaches that last puff and must get back to work, or the drunkard who lays down in bed knowing that when they wake up life will be back to it's aberrant normality.
The only cause I could find for this malady (and I think it is a malady) was that I was living for the weekend, as it were. If one accepts without remorse or regret the way things currently are, one can set about changing them, but if one holds onto old negativity, things will not improve. Happiness is not something one should aim at, rather one should learn to take the good with the bad.
Another thing I like to do when I'm feeling insecure is to analyse how I came to be where I am: what important decisions did I make to get here, what was I thinking at the time? To say that one wishes one had done differently is usually not true, because usually one did what one thought was right at the time, whatever that is, or at least one had convincing reasons at the time, even if they turned out to be wrong. If they were wrong, now is the time to learn from those experiences, but one can hardly learn from and apply experience if one is not prepared to move onward.
Change is a part of life, each life is a process of change and change is something to accept. The past is the past and it should be let go of. By accepting that things are the way they are, that nothing can be done to change them and historical review can only serve to prepare one for the future, and then to live through the change that is living, I think one can be perpetually happy. Conversely, if one does not accept that things are as they are and can't be changed, or one does not accept that things won't improve by themselves and shouldn't be run away from, I then think one is doomed to seek to escape the reality of one's situation.
I don't know about physiological mechanisms or whatever, but I expect it would work like a nicotine patch: supposedly it would give one temporary relief so that one could wean themselves off their bad habit, but I think this could only happen if one identifies what that bad habit is, and of course if one merely substitutes the new source of relief for the old, no improvement will be found.