What are some of the most common organic (non-psychiatric) reasons for insomnia?

Pulmonary and cardia: Chronic pain, COPD , CHF , sleep apnea and CNS disoders.

Insomnia: It is very possible that insomnia is the most common symptom of all. It could be related to multiple causes, linked to medical illnesses or psychological factors, and most commonly due to disruption of the circadian rhythm and sleep cycle, like in jet lag or work shift issues. If not due to major illness, it will solve with a regular bedtime and wake time, exercise, diet, relaxation routine.

Organic insomnia: The most common causes would be poor sleep hygiene, and uncomfortable sleep environment that is not conducive to sleep, sleeping with a noisy bed partner, sleeping with pets in your bed. Organic causes would be sleep apnea, circadian rhythm sleep disorders, periodic limb movements of sleep, upper airway resistance syndrome, chronic pain, diabetes with frequent urination, hyperthyroidism with nighttime sweats.Any of a variety of endocrine disorders, breathing difficulties causing loss of oxygen during the night not related to sleep apnea, parkinson's disease, multiple sclerosis, congestive heart failure, drug and alcohol abuse.Those are the ones that come to mind off the top of my head.Gastroesophageal reflux disease would be another cause. Hope this helps. Best wishes.