Is it possible to "naturally" reach the first three jhanas

Is it possible, having been taught meditation by a zen master, to **naturally** enter the 1st three jhanas. By that, I mean through mental effort which is not really meditation as we normally think of it (seated or walking, *all* effort being applied to that). I ask because the 1st three jhanas seem, *potentially*, much more mundane than the rest, worldly. e.g. I feel pretty strong sensations of pleasure *most of the time*, as long as I'm not there and then planning to *do* something. If that second paragraph seems *super* delusional, then how close is dhyana to a pleasure in which you can't identify *why* you feel good?