I have been in the zone repeatedly, and done so for ... a decade at least I think. But I'm continually learning about my body, what I need, etc, the whole time. It is a lifelong learning experience--I'll only stop learning when I die!!
So here's my own experiences, take from it what you want, let go of the rest. :-)
When I'm fully in the zone, I really feel it. My energy shoots up. I'm more mentally alert even if I haven't had as much sleep as I'd like to; I'm more able to absorb information. I feel better physically. I have more stamina. I become more active physically naturally--it just happens by itself, as a direct result of the diet. (Many people find they have the same experience I believe--that they go on this diet, they get in the zone, and then they naturally start being more physically active. It's because they no longer feel lethargic because of the food I think.) I feel the change probably several days after I start zoning, if I've fallen off the zone. And I've fallen off many times!! If it's just one small misstep, or several missteps, it may be a shorter time before I feel the energy coursing through my veins again.
And one way I know I'm going into the zone, by the way, is when I'm still drinking the same amount of water, BUT, my body has started using the water somehow, I forgot the scientific explanation for it, and suddenly my urine becomes a lot more dark yellow, on the same amount of water per day, and I end up having to drink a lot more in order to have light or clear urine. So it's an odd feeling because I go into the zone and suddenly I'm not peeing that much anymore.
Anyway. I have experienced this remarkable energy when I was 192 lbs, so I was 60 lbs overweight and still very energetic, still not having many colds etc., and I'm 130-135 lbs now (and the weight loss is due to the zone diet by the way--no other diet has worked for me like the zone diet has!), and I still experience this very particular energy that I have come to call "that zone energy." I will be honest--I don't think I felt very different when I was in the zone at 192 than now when I am 130 (actually, 132 the last time I looked, but anyway ...)
When I was going without much sleep this past summer because of very severe congestion that blocked my breathing, very severe allergies, reflux (phelgm coming up to block my breathing), my heart stopping periodically or frequently, my breathing stopping periodically or frequently---and these breath- and heart-stopping start happening when I try to sleep, and they happen during the day too when I'm not trying to sleep, and I have gone as little as 1 hour per day of sleep due to all of these problems, and it has gone on for weeks--the zone diet was what helped give me the energy to research, to get help, to exercise even though I was terribly sleep-deprived, etc., etc., etc.
I think at one point I was averaging two hours of actual sleep per night for a week or two, and I am not exaggerating ... I was keeping a notebook and writing down how much I slept. I have mild sleep apnea it turns out, and getting the Holter monitor to monitor my heart next week. I have gone as long as 3 nights and 3 days, roughly, with absolutely no sleep at all, and again, not exaggerating--it was that bad.
I am vastly better now physically, all of the above have gone down dramatically, for a variety of reasons, including drastic lifestyle changes, and NAET treatments (http://www.naet.com).
I now sleep 6-9 hours a night, although my sleep apnea obviously affects the quality of my sleep.
But, I keep falling off the diet now that I'm far better, and I learn from it that, well, I still feel so much better when I'm zoning than when I fall off, so I keep exploring the good reasons why I fall off (emotional eating, etc) and exploring alternatives to emotional eating (e.g., drinking two teas that are very intense-tasting to satisfy my need for something intense). Also, too, I need to find ways to heal my emotional eating.
Oh, another sign that I'm in the zone. I no longer have "carbohydrate cravings." I have gone months and absolutely no cravings. It's hard to describe, but
I find when I eat a lot of refined carbs, e.g., pasta, that I feel very pleasantly ... lethargic. It's not a bad feeling. It's serotonin I think, triggered by the bread and carbs and so forth. BUT, this experience makes me sluggish, less alert obviously, makes me just want to sink into my Lazy Boy chair or coach and watch TV and do nothing. When I'm in the zone, I'm much more inclined to DO things.
My "emotional eating" is not the same as "carbohydrate cravings." The two feels different to me. The emotional eating is more for ... well, I have a lot trauma to heal, and I'm healing, slowly, and thankful that I'm healing, and there are days when I get triggered and then I need comfort food. But when I do emotional eating, I tend to eat stuff now like ... coconut flakes with cocoa and fructose and salt and olive oil all mixed up--very tasty for me--or a combination of nut butters (cashew butter, almond butter, peanut butter) mixed up with a little banana and so forth--also tasty, but I try to limit this kind of eating to only several times a week and stick to teas (Bengal tea is one example of an intense-tasting tea) the rest of the time ...
Hope this helps!!! It's my personal story, and I can't speak for you obviously--your experience may be different--but hopefully, you will have kind of the same experience--that even though you're sleep deprived, you'll still experience increased energy and mental alertness and so forth anyway.