Yes, this state of mind could be called a "flow". Regardless of how we call it, "flow" or "bliss" or "sheer joy" or "connection with the Source" as it is referred to in the New Age circles, the idea is clear, the choice of words is just our personal preference.

And, yes, those states do vary in their length and intensity and they are certainly not permanent. However, as I know from my personal experience, they do build up a momentum of energy that makes it easier to move into that state the next time and the next time and again and again. Thus I can evoke them more frequently and, eventually, creating joy or bliss or however you want to call it becomes a part my general life style. So, though that state of mind itself is impermanent, the life style that evokes it more or less frequently becomes permanent. I started doing this about a year and a half ago meaning that I allowed myself to do what my "inner child" wants to do RIGHT NOW IN THE MOMENT. There are moments when if I feel like painting or drawing or writing or swimming or making jewelry RIGHT NOW and I listen to that inner call. I drop everything, all the "responsibilities", all the things I am "supposed to" do today and follow that call, and it feels like I am literally allowing myself to finally "get a life". I don't do it as often as I want to but I try to allow myself to do it as often as I can.

I'd like to get to the point where one of my interests a.k.a "passions" can turn into a vocation (not permanent and not full time but something that could give me a sustained fulfillment). This, I feel, would be a nice point where the state of "bliss" could be combined with some commitment. I certainly agree that the "blissful" state of mind is transient, it comes and goes, but if it becomes a part of some relatively stable occupation then all unpleasant duties attached to it can be carried out without much struggle. Or the struggle becomes so much easier to handle. Like, for instance, if I enjoy taking care of animals in the animal shelter, then even if I don't like certain parts of that work, I'd still happily accept it as part of the "package" because connecting with beautiful innocent creatures would be more than enough compensation for any inconvenience or any crappy duties that may become a necessary part of the whole experience.