It's not enough for people to sleep eight hours a day to feel well-rested. Sometimes, surprising factors affect people's energy levels and make them feel tired.

But what are these factors? Refinery 29 has compiled a list of culprits that zap out people's energies.

The first of these is not drinking enough water. When people are dehydrated, they find it hard to stay concentrated and maintain a good mood.

Another reason is a messy environment. When people's bedrooms and work areas are not in order, it can make it difficult for them to concentrate. Because of this, people waste their resources being distracted by their mess.

Third, people also waste energy staying mad at their significant others. A new research revealed that people who have partners who are responsive to relationship issues tend to be more well-rested than those who don't.

Fourth, people who skip their exercise routines might feel something off-key about their day. Health buffs who regularly work out tend to sleep better, so missing this might cause people to feel more tired than usual.

Allergies are another reason for feeling sluggish. Not everybody experience having allergies until later in life, so they might be surprised how the usual symptoms — runny nose, itchy eyes, to name a few — affects their bodies.

It also might seem like a good idea to sleep in over the weekend, but disrupting the body's sleeping cycle has its negative effects. It is highly recommended that people fall asleep and wake up at the same time every day, even during weekends.

The seventh culprit for tiredness is not getting enough iron. Iron is needed for the blood to keep moving and carry oxygen to the muscles. People who feel unusually tired might do well to eat leafy greens, tuna, and legumes.

Generally, smokers face difficulty sleeping. Nicotine, which is found in cigarettes, is a stimulant that gives smokers a fleeting sense of energy. On the flip side, the lungs and hearts of long-term smokers face a more difficult time to function, therefore making people feel tired all the time.

Another surprising energy-zapper is snoring. Snoring isn't always a bad thing, but it can be a sign of sleep apnea — a disorder in which one's breathing stops momentarily while one sleeps. It causes one to wake up feeling tired and feeling sleepy all day.

Lastly, taking cold showers might seem like a great idea to feel refreshed and energised, but warm showers are more recommended.