Love is one of the most complex and mysterious human emotions. It’s also one of the most universal. Everyone on earth has loved someone at some point in their lives. Love comes in many different forms and is a hugely important part of our lives.

Some people define love as a feeling of affection and attachment to another person. Others use the word to describe a deeper commitment, such as a marriage or a romantic relationship. Still others use the term to describe a spiritual or religious experience. The word love has been a topic of discussion for millennia and is a subject of study in psychology, anthropology, philosophy, sociology, and other fields.

Whether you’re in love with your partner, your pet, or your freedom, all of these experiences are different forms of love. In a recent survey, people described their feelings of love in terms of physical sensations and emotional patterns. They talked about the way they felt when they fell in love, the feeling of being a whole when with their loved ones, and the energy of reaching out and interacting with others. Some of the most common types of love were romantic, friendship, family, and a sense of global community.

When a person feels in love, it can feel like walking on air or floating in a cloud and as sweet as strawberry cotton candy. But when the feelings of love begin to wane, it can feel like wallowing in a muddy pit of self-pity or like you’ll never climb out of the bottom of a broken heart.

The experience of love can be complicated by a number of factors, including insecurity and jealousy, miscommunications, or life changes. But with open communication and effort, love can deepen and withstand the test of time.

A major challenge in defining love is that it’s not exactly an emotion. The classic textbook on emotions, by Paul Ekman, defines an emotion as a particular set of facial expressions or behavior that occur together and are experienced consistently by the same person at the same time. But there’s a lot more to love than just a set of emotions or a specific behavior, and psychologists have been debating what it means to say you’re in love for decades.

Throughout history, philosophers and religious leaders have theorized about the nature of love and relationships, but it was only in the 20th century that psychologists began to study the phenomenon in earnest. The field of psychology is still learning about the complexity of love, but anthropology, biology, and other disciplines have contributed to our understanding of this profound and complicated emotion.

For most people, sleep seems like a simple process—you get comfy, close your eyes and drift off to rest. But researchers have found that the brain and body continue to work while you slumber, making sleep one of the most complex and mysterious body processes known to science. In fact, it’s so important to your physical health that there is an entire field of medicine devoted to understanding and treating sleep disorders.

Inadequate sleep has been linked to many health problems, including heart disease and stroke, high blood pressure, diabetes, depression, obesity and even dementia. Insufficient sleep may also impair your ability to think, learn and react during the day, and can affect your mood, energy level and performance at school or work. Getting enough restful sleep can help you maintain a healthy weight, manage chronic health conditions, improve your immune system and boost your mental sharpness.

There are a number of theories on why humans need to sleep, but scientists are still trying to figure out exactly what happens during sleep and why it’s so important. For starters, all mammals—and nearly all animals in general—sleep. While this may seem obvious, scientists haven’t figured out exactly why animals sleep and how it helps them survive.

During sleep, a region of the brain called the hypothalamus initiates a series of changes in your body that prepare you for slumber. For example, your body’s muscle activity slows down and electrical activity in the brain starts to decrease. These changes, and the ones that follow as sleep continues, affect every cell in the body.

In addition to its many other functions, some research suggests that sleep plays a role in how your memory works, and may be important for the formation of new memories. A study of mice showed that when the animals were deprived of sleep, their bodies produced more of the proteins that are linked to Alzheimer’s disease. The good news is that getting more sleep reduces the levels of these proteins in the brain.

It also appears that sleep influences your metabolism and immune system, and can influence how fast you lose weight or gain weight. A study of men and women who followed their sleep patterns for a long time found that those with longer periods of uninterrupted sleep lost more weight than those who didn’t.

Getting adequate amounts of quality sleep on a regular basis isn’t always easy, especially during times of stress or when you have a challenging schedule. Prioritizing healthy sleep habits can be difficult, but the payoff is significant: getting enough restful sleep on a regular basis is linked to a stronger mind and body, improved cognitive function, lessened risk of health issues and an overall sense of well-being. And if that’s not reason enough to get enough sleep, consider this: Researchers have shown that sleep deprivation is associated with poorer performance at work and in school and a higher risk of accidents. It’s time to wake up to the importance of sleep.