Not at all. Not even close. Ever been put under for surgery? Lights out, you immediately fall into a deep sleep. Even if you were aware, which you won't be, there's no "gasping" or changing colors... naturally a loss of color as you become hypotensive, but nothing as dramatic as what you're describing. Your respirations simply become more shallow and further apart until they stop.
I'm going to just *tentatively* disagree with heartless_95, with the provision that you are willing to do a fair amount of studying and prep. If this is well-researched -- and there are others on this forum who are more well-versed in H than I am-- I believe even a first-timer could pull this off. Again, provided that you really do your homework, up to and including practicing self-administered IV injection. This would be my personal method of choice, because it's pain free and virtually guaranteed if done right.
Yes. Beyond euphoric. Imagine a warm glow that radiates from your belly to gently envelope you, like absinthe-infused ectoplasm.