I spoke today with a very nice lady who has struggled with insomnia for years, knows she is hooked on sleeping pills, and has OSA but is finding her CPAP use limited by the time she spends awake at night, tossing and turning. Turns out she is drinking at least 24 ounces of caffeine every morning, which she didn't think was a problem because she USED to drink a whole pot of coffee daily and because she doesn't drink any later in the day. I explained the concept of a "half life" to her, and how only half of the caffeine is gone every 10 hours. 400mg of caffeine at 8am results in 200mg of caffeine floating around at 6pm and 100mg of caffeine still there at 4am. Caffeinated 24 hours per day.
And doing your ironing at 2am or watching TV at 3am does not help. The term we use to describe activities that help sleep (and do not hinder it) is "sleep hygiene"; not a lovely term but managing your sleep hygiene means better sleep. Regular bed times and rise times, skipping caffeine and alcohol and antihistamines, de-stressing before bedtime, avoiding light/exercise/mental activity in the middle of the night are all pro-sleep activities.