Feel the same. I doubt that it's 3-4 seconds, because I loose the sense of time too, but dunno about you. Hmm, isn't seconds sleep very similar to that too? I would even say that it's much more extreme. I can hang in-between reality and dream for minutes in the worst case, until I either wake-up unpleasantly or doze off.
I'm awake enough when it's happening that I don't think I'm in "sleep time" yet. It's actually a bit disturbing. I say this accounting for the fact that this is all pretty hard to tell about what time it is, but, part of the reason why I noticed it is that it seems to be happening much earlier than I'm used to.
(It's terrifying what your brain does in sleep....)