How sleep works
Two systems decide when you feel sleepy. Most of what CBT for insomnia does is give them a chance to line up again.
Sleep drive
From the moment you wake up, a pressure to sleep starts building. It grows the longer you’re awake and drains away while you sleep. Researchers call it sleep drive, or the homeostatic process.
Sleep drive is why a long day can end in deep sleep, and why a late nap or sleeping in late can leave you wide awake at bedtime. Anything that lets you sleep earlier or longer spends some of the drive you’d otherwise carry into the night.
You can’t force sleep drive to build faster. You can stop draining it. Extra time in bed, dozing in the evening, and naps all take a little off the top.
The body clock
The second system is a clock in the brain that runs on a cycle of about 24 hours. It sets a rhythm of alertness through the day, and it’s set mostly by light, especially morning light, and by when you get up.
The clock is why many people get a second wind in the evening, and why sleeping in on the weekend can make Sunday night hard. Get up two hours later and the clock shifts later too.
A wake time that stays the same every day, weekends included, is one of the strongest signals you can give the clock. That’s why the sleep window starts with one.
When the two line up
Sleep comes most easily when sleep drive is high and the clock has moved into its night. Lying down earlier than both are ready usually means lying awake.
How insomnia keeps itself going
Insomnia often starts with something real, like stress, illness, pain, a new baby, or a change in schedule. Then it can outlast the cause. One common reason is that the ways people cope make sense in the moment and work against them over time.
- Going to bed earlier, or staying in bed later, to catch up. This spreads a smaller amount of sleep over more hours and lowers sleep drive.
- Lying in bed awake for long stretches. The bed can start to feel like a place for worrying instead of sleeping.
- Napping, or dozing on the couch in the evening.
- Watching the clock and counting how much sleep is left.
- Trying hard to sleep. Effort tends to wake people up.
None of this is a personal failing. It’s what most people do. The tools in Sleep Toolbox work on these habits directly.
Sleep changes across life
Sleep gets lighter with age, and waking briefly in the night is normal at any age. Most people wake several times a night and don’t remember it. How much sleep someone needs also varies from person to person. There is no single number everyone should reach.
References
- Borbély, A. A. (1982). A two process model of sleep regulation. Human Neurobiology, 1(3), 195–204.
- Harvey, A. G. (2002). A cognitive model of insomnia. Behaviour Research and Therapy, 40(8), 869–893. doi.org/10.1016/S0005-7967(01)00061-4
- Riemann, D., Espie, C. A., Altena, E., et al. (2023). The European Insomnia Guideline: An update on the diagnosis and treatment of insomnia 2023. Journal of Sleep Research, 32(6), e14035. doi.org/10.1111/jsr.14035
Helpful links
Everyday Insight’s tools are for education and personal reflection. They are not therapy or medical care, and they are not for emergencies. In an emergency, call 911. If you are in crisis in the United States, call or text 988.