Two dogs sleeping
Insomnia is where you might feel that you are not getting enough sleep at night, have difficulty falling asleep - wake up at night frequently or very early in the morning.
Not having enough quality sleep can lead to a cycle of feelings of irritability and worry about why you are unable to sleep and thus leading to poor sleep.
Short-term and temporary insomnia, maybe caused by jet lag or a one-off stressful event which lasts for only a few days is usually not a cause for concern. Long term; lasting for many weeks, months or possibly years does need to be addressed.
Common causes are; stress, anxiety and depression - noise - uncomfortable sleeping environments with rooms that are too hot or cold - substandard beds - alcohol, caffeine or nicotine - recreational drugs or prescribed drugs - shift work - eating, drinking  or to much tech time close to bedtime.
Whatever the reason for sleep loss it can affect you both mentally and physically, as it is an important part of your daily routine and essential for your health and survival as a balanced diet and water are.
Not having enough quality sleep is a strong indicator of declining mental health as you may find it difficult to cope during the day with having negative thoughts and less able to rationalise irrational thoughts, difficulties and concerns.
A good nights sleep is often the best way to help you to cope with problem solving, coping with life's stresses and to recover from illness. Chronic lack increases the risk of disorders such as high blood pressure, cardiovascular disease, diabetes, depression and obesity.