5. Dehydration
Many of us forget to drink sufficient amount of water while running around to keep up with our hectic lifestyle, thus resulting to the lethargic feeling. Severe dehydration occurs in our body without giving us much indication except for the numbing tiredness and sometimes nausea.
Fix
Minimum 8-10 glasses of water every day is a must. You might even need more if your job is more physically demanding than average. If you have a habit of drinking caffeinated products, you might need to compensate that with a few more glasses of water.