Your extreme fatigue might be coming from one of these energy suckers. Read on to find out the 5 surprising culprits. 1. Dehydration It turns out that even moderate dehydration (which results in the loss of 3 percent of your body weight) can make you feel mentally sluggish and mess with your concentration. The next time you\'re feeling foggy or lightheaded, don\'t just assume you\'re in serious need of some food. Try downing a glass or two of water. 2. Cell Phones Checking your cell before bed amps up brain activity, making it harder to doze off. Plus, any electronic gadget\'s artificial blue light can suppress the sleep hormone melatonin. A 2011 poll by the National Sleep Foundation found that 20 percent of people ages 19 to 29 are awakened by a call, text, or e-mail at least a few nights a week. Power it down well before bedtime. 3. Medication Many drugs have veiled energy-sapping side effects. Chief among them are some classes of antidepressants and certain beta-blockers used to prevent migraines or treat high blood pressure. If you start a new med and feel more lethargic than usual, see your doctor for an alternative. (If there isn\'t one, take your dose right before bed.) 4. Overtraining While working out zaps the stress hormone cortisol, prolonged sweat sessions-like, for example, regularly running for more than 30 minutes at a steady rate-can actually rev cortisol production. Interval training (bursts of intense activity) combined with strength training (free-weight and body-weight moves) helps keep cortisol in check. 5. Low Iron The mineral shuttles oxygen around your body and removes waste from your cells. If you\'re not getting around 18 milligrams a day, your body struggles to function properly and you can feel worn out; low iron levels in your diet can cause iron deficiency anemia. If you feel sluggish, ask your doctor for a simple blood test to see if you should be taking a supplement.