Insomnia has several possible causes, including stress, medical conditions, environmental changes and ingested substances, according to Mayo Clinic. Stress and anxiety prevent people from relaxing. Typical concerns that interfere with sleep are work, family, health and school.
Medical conditions that cause chronic pain, breathing difficulties or frequent urination interrupt sleep, Mayo Clinic reports. Disorders that cause insomnia include depression, arthritis, cancer, heart failure and lung disease. Examples of changes that throw off people's internal clocks are traveling and switching to early or late work shifts. Oral medications, such as antidepressants and heart, blood pressure or allergy medications, keep some people awake at night. Nicotine, alcohol and caffeinated foods and drinks work as stimulants and lead to insomnia.