I've had the same kind of experience since I started college -- my life's had the pattern of "work hard for several days, then recharge for several days," and the recharging days suck -- and although sleep and exercise help a bit I haven't been able to substantially reduce the amount of time I need to bounce back from the slumps. Until now, at least.

At the end of this past summer I took a meditation course with dhamma.org, and three weeks ago I started meditating again. (I went on the retreat for unrelated reasons -- mostly I was thinking, "Ten days doing absolutely nothing, that's crazy, maybe something really amazing will happen to my brain" -- and when I finished it I was, at first, mildly disappointed with the results, so I didn't keep meditating.)

Anyway, meditation has had a really pronounced effect on my overall level of mental energy. I only have three weeks of data so I can't say decisively what it can and can't do, but an hour of meditation seems to cancel out a day or two of accumulated burnout. I'm starting to think that meditation could be literally life-changing on a large scale for me. (Incidentally, it's also unbelievably effective at eliminating stress. I'm actually much more certain of its efficacy as stress-reducer than as energy-replenisher.)

I definitely think you should try out a meditation course next time you have ten days free -- it could really do you some good.