Why the First Weeks of CBT-I Can Feel Harder (and What Is Normal)

PLACEHOLDER: founder to supply the final article. The structure, internal links and CTA are real; the prose is illustrative and claims-safe.

What people commonly notice early on

Cognitive behavioural therapy for insomnia (CBT-I) uses no pills, so people are often surprised that it can have side effects. Most of them come from one part: the sleep window, also called sleep restriction.

In the first week or two, people often report:

• feeling sleepier than usual in the day
• tiredness and low energy
• being short-tempered
• headaches
• finding it harder to concentrate

For many people, this is the toughest stretch of the whole course.

Why it happens

A sleep window shortens your time in bed so it sits closer to the sleep you are getting. The idea is to build up sleep drive, the natural pressure to sleep that grows the longer you are awake. Stronger sleep drive tends to make sleep come faster and hold together better.

The cost is that, for a while, you may sleep a little less than before. Your body notices that in the day. The window is then widened in small steps as your nights settle.

What the research found

Kyle and colleagues (2014) measured people in the early weeks of sleep restriction. They found more daytime sleepiness and slower reaction times during those strict early weeks, when time in bed was at its shortest.

Later work looks at the wider picture. A 2021 review of trials found that sleep restriction helped with insomnia severity overall. The HABIT trial (2023) tested it in UK GP surgeries, delivered by practice nurses. These findings are about the approach in general, not about any one course or app.

Driving and safety-critical work

Feeling drowsy behind the wheel is dangerous. If you feel sleepy, do not drive, cycle on busy roads or operate machinery. Plan lifts or public transport for the first fortnight if you can.

If your job involves driving, heights, heavy machinery or caring for others in a way where a lapse could hurt someone, talk to a clinician before you start a sleep window. They may suggest a gentler version or a different starting point.

Who should talk to a clinician first

A sleep window is not suitable for everyone to start alone. It sits behind a safety check, and you should speak to a clinician before using it if any of these apply:

• you are under 18
• you have bipolar disorder
• you have epilepsy
• you are pregnant
• you have, or might have, sleep apnoea
• you do safety-critical work

This list is a reason to have a conversation. It does not say what is right for you. Our free self-check covers some of the sleep apnoea signs worth raising.

Keeping going

A few things tend to make the early weeks easier:

• Keep the same wake time every day, weekends included.
• Never take the window below a safety floor, however short your nights have been.
• Change the window in small steps, once a week, and only after the safety check.
• Plan easy days at the start, with less driving and fewer late evenings.

The sleep window explainer shows how the window is set and adjusted.

When to stop and ask for help

Pause and speak to a GP if the sleepiness feels unsafe, if your mood drops sharply, or if you feel high, wired or unusually energetic. Do the same if things are getting worse after several weeks rather than settling. Stopping is fine. You can come back to it with a clinician's advice. For a realistic sense of timing, read how long CBT-I takes.