We're in the midst of an energy crisis. No, not that one. This one: We're tired. So. Completely. Tired.

To paraphrase Aerosmith, it can often feel like your get up and go musta got up and went. It's not just a matter of working too much and sleeping too little, though of course those are both big parts of it.

It's sometimes easy to pinpoint why you're flagging by the afternoon -- that weekend of partying, for instance -- but sometimes the causes are more complicated.

Here are some common contributors to that two o'clock feeling:

You're not sleeping enough

OK. So this one is kind of a gimme, but not for the reason you think. Sleep isn't just about resting; there's a lot going on inside while you're conked out for the night. Case in point: human growth hormone. Growth hormone, a protein made by the pituitary gland, plays a role in making muscles healthy and bones strong.

It affects how our bodies collect fat (especially around the stomach area) and it helps balance the ratio of good to bad cholesterol. It's also essential for normal brain function. Not enough it of leads to fatigue, decreased strength and stamina, and depression symptoms.

Since growth hormone is secreted primarily when we sleep, seven and a half or eight hours of high-quality shut-eye each night will help keep weight and pain down and boost up your energy.

You're eating too much junk

We think of sugar as a quick way to boost energy, but in the long run it does just the opposite. All those that end in -ose, like glucose, dextrose, maltose and sucrose, are just going to leave you sluggish. Research shows that fast food also puts you in biological slo-mo. Try this all-day energy meal plan, instead.

You're not drinking enough water

Many people can't identify when their fatigue is due to dehydration. A glass of water may be the jolt you need, rather than sugar (see above). Drink as much H2O as it takes to keep your mouth moist throughout the day.

And remember this rule of thumb: Your pee should be light yellow to clear. If it's brighter and darker yellow, you need to drink more water.

You're low in vitamin B

You need B vitamins for your mitochondria to turn glucose into energy. We can absorb B vitamins well in liquid or pill form, but 99 percent of us don't get enough from our diets.

Try taking a vitamin in the morning and evening. This will keep levels stable and get you energized, and there's no harm in it since you'll excrete any excess water-soluble vitamins.

If you're having symptoms of low energy, check your vitamin B12 and D levels, and, in any case, have them checked annually. If you find you have the rare case of not absorbing them well into your intestine and stomach, you can get a B12 injection yearly.

You've got an infection

Infection and inflammation can be two dominos in the low-energy cascade of symptoms. One of your goals could be to monitor your body so infections don't linger. So what can you do? Floss regularly to lower your gum inflammation risk.

Reduce sinusitis with a neti pot. Use probiotics to treat prostatitis, vaginitis and bowel infections. With viral infections, frequent hand washing, sleeping and avoiding saturated fats and simple sugars can help.

You need to move more

You can jump-start your energy with an activity as simple as walking. When you get moving, nitric oxide is released from the artery linings to allow blood to move freely through your vessels.

This helps get more nutrients to your cells. Your body responds to your actions. If you tell your body you're watching re-runs all night, it will downshift energy production. If you tell your body that you need to have a brisk morning walk, it responds by giving you the energy you need to do just that.

Your hormones are out of whack

There are numerous hormones that factor in to how energized or blah you're feeling. Hormones are like dimmers on headlights. When you need bright lights, you turn on certain hormones to increase the energy to that area, and decrease usage elsewhere. The fine-tuning starts in your hypothalamus and pituitary.

The two primary sources of trouble are slow-functioning thyroid and adrenal glands. As for adrenal hormones, take this little test: When you're hungry, do you quickly switch to feeling so irritable and ravenous that if you don't eat, you'll commit a felony? This is a sign that your adrenal glands may not be working properly.

You're insulin resistant Insulin resistance -- a precursor to diabetes -- makes it hard to get sugar (our body's fuel) to our energy production plants. We then distribute the sugar into fat storage rather than storing it in cells, which need it to produce energy.