I can speak in tongues -- an ability picked up back in my charismatic/pentacostal days (long since left behind). I left that religious milieu but the ability stayed on. So I can give a first-hand account, from the inside and from the outside, as it were.

From the inside: there is nothing 'ecstatic' about doing it -- no emotional change, no feeling of anything different. In that respect it's like scratching somebody else's itch -- I don't even feel it. But it's definitely not something that I am consciously doing, other than deciding when to stop and start. I'm not making any decisions about what noises come out; they seem to come of their own accord without any "help" from me. I've tried to "steer" the output toward different patterns, etc., but with marginal success. The flow of sounds appears to have a mind of its own. (I hope not literally!)

From the outside, so to speak, it sounds a lot like gibberish, with a lot fewer vowel and consonant sounds than English. There are patterns that repeat but I doubt that means anything. I certainly can't map any part of it onto any meanings -- it's all equally meaningless. I doubt the phenomenon means anything at all -- some bizarre pattern of random noise in the speech centers of the brain, perhaps left over from some unknown and unknowable use in our far-distant ancestors. Maybe it's something that some people can do and some can't, like rolling your tongue. It's certainly not a language and it makes no sense, at least to me, to conflate it with idioglossia.

I've heard that there are people outside the Christian religion who do what appears to be identical to "speaking in tongues" -- that's why I think it's a latent ability in the speech centers of the brain, that gets tapped into somehow by people in certain states of mind or such.