I am a big fan of nutritional therapy to correct disease/disorder, including mood problems. Just correcting a deficiency can create elated feelings.
Niacin is probably my favorite thing to take when I'm feeling blah. Just take about 100 mg or more of niacin (not niacinamide or flush-free niacin - you want the flush). If you can only find the time-release kind, open up the capsule and chew the beads. Reduce dosage next time if the flush lasts more than an hour. Niacin may be taken multiple times a day. The flush may be uncomfortable at first, but I've learned to love it - it's like I can feel my blood delivering delicious nutrients all over my body.
Iodine therapy also helps if you are deficient. Bromide detox is a pain, but salt loading helps, as does taking it slow.
Magnesium is also a good one to make sure you're getting enough of if you're feeling blah.
Mood Cure by Julia Ross is an excellent resource that includes a recommended list of vitamins and supplements for varying degrees of stress, depression, or just blah. I highly recommend it.
DoctorYourself.com is also a great resource for DIY nutritional therapy.
I will also add that there is no high like ketosis high. Fat-burning rather than sugar-burning gives this constant energy and euphoria that just doesn't quit (once you get past the detox - salt helps). I love a good fat fast. Though if you're not overweight, paleo might be a better option.