Thank you for that reply. I've certainly never experienced anything like that in goodness knows how many hours, although I've read theoretical descriptions of the jhanas.

There's a general convention that one does not ask about another person's meditation experience, nor speak of one's own except with one's instructor. In fact, people attending meditation class are sometimes advised not to discuss their experience with each other, which does not make for epistemic hygiene around the subject. I hope that on LW we need not be constrained by that (nor, of course, obligated to speak of these things).