I get this "in the zone" feeling you're talking about approx. once every week.
I usually go through a week like so:
1. Brood about being lonely
2. Brood about doing nothing else but studying and computer'ing
3. Procrastinate throughout 1 & 2, leaving deadlines for the end
4. Realize that yet another week has become hectic enough, if only due to my procrastinating and NOT due to the workload
5. Start doing some studying, start cathing up deadlines for exercises/projects/presentations/essays
6. Sequentially finish (not always :-)) the tasks at hand, hand in pending stuff
7. Feel really good about getting the job done
8. Start studying/working on favorite subject/project
9. Get in the zone for 1-2 days, where being lonely just becomes an advantage, rather than something to gripe about
10. Complete workload successfully, weekend is here
11. Do almost nothing, waste time, procrastinate instead of planning
12. GOTO 1.
But I tell you, there are times when I get back home after a loooong day at the uni at 23:00 and I just feel invincible. I'm walking on the road and feel like everyone makes way for me to pass, as if I'm flowing through the people going the other direction... I feel I'm so cool, I could hit on ANY girl right there and succeed. I catch the bus on time, I am super-efficient and have ultra-high self-esteem (NOT usually the case). I find listening to music makes the "in the zone" feeling stronger. Then, when I come back home, I'm just full, like there's nothing more to do today that would make me feel better about myself. As if problems have just ceased to exist or start existing
It's an interesting question though; is it possible to induce this mindset at will? Hmmm... (and plz don't mention drugs, I don't do drugs) What about caffeine? Doing something wild (but not overtly stupid)?
Now, if I could start abstaining from procrastination, everything would be perfect....