Sadly, since I was a kid (as long as I can remember).
Recent visit with sleep specialist has determined that the most likely cause is thinking too much while in bed. I typically review what went on during the day, plan the following day/week, or "daydream" about things that I was too busy to address during the day. Doctor said that highly active thought processes are a primary cause of insomnia.
I'm currently trying to get my insurance company to cover a sleep study, primarily do determine if I have apnea (family history of this). A side benefit may be a cure to my snoring, which is so loud, that I sleep in a different room so that my wife can get some sleep at night.
Have periodically used sleep medication (non-prescription, like Tylenol PM), but psycological dependence is a potential problem.
In spite of all the difficulty I have had getting to sleep over the years (It would typically take 3-5 hours to fall asleep), Doctor suggested something that actually works.
Count backwards from 1000, by 7's. If this is too easy, count backwards by 17. The idea is to occupy the mind with a task, but with a task that is meaningless, thus allowing the brain to shut down.
I scoffed when the Dr. suggested it, but it has worked wonders for me. While I will periodically have trouble falling asleep, I am usually out in 15-20 minutes. A significant improvement!
Hope this helps!
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TaxPhd
"Those who live by the sword are probably pretty f***ing good at it."
"Instructions for a successful gunfight: Front Sight, Press Trigger, repeat
as necessary." - B. Braxton