This project aims to elucidate whether CBCTi changes symptom severity or even remission of anxiety disorders as compared with a delayed-start control group. The investigators will use a delayed-start randomized controlled trial in a cohort of individuals with anxiety and insomnia (N=98) to compare the effects of an online therapist-guided cognitive behavioural and circadian therapy for insomnia versus control on overnight emotion regulation and mental health outcomes.

The project will involve at-home assessments and in-lab visits. At-home assessment involves recording sleep and circadian rhythm measures with wearables and daily diaries. Participants will be invited to perform two sleep studies and neuroimaging sessions to investigate the effects of CBCTi on neuroimaging and psychophysiological markers of overnight regulation of emotional distress.

This study is a delayed-start randomized controlled trial comparing the effects of online therapist-guided cognitive behavioural and circadian therapy for insomnia (CBCTi) versus control on emotional regulation and mental health outcomes.

To be enrolled in the study, the participants are required to complete an online prescreening survey followed by a telephone screening interview with further questions and to verbally explain to participants what is required of them in this study. After an interview screening, the participants will receive a finger-pulse oximeter by mail to screen for the presence of obstructive sleep apnoea (3 nights at-home). The device is then returned by pre-paid mail and the recording is analysed to screen for moderate to severe sleep apnoea (oxygen desaturation index ≥ 10). If eligible, the participant will be invited to the Woolcock Institute for a screening visit.

The screening visit starts with a consult with a clinician/physician who performs a medical screening, explains the study, answers questions and addresses concerns, and obtains written informed consent. At the end of the consult, all eligibility criteria have been evaluated and eligible participants are assigned a randomization number i.e., allocated to either the immediate CBCTi-arm or the delayed-start control-arm. The treatment arm consists of an online therapist-guided CBCTi intervention which comprises online sessions to be completed in 8 weeks. Participants in the delayed-start control arm in this study will not receive any active intervention during the first two months but will be offered the same therapist-guided CBCTi program thereafter

During the screening visit, participants will be asked to perform in an audio-visual recording while singing along to "Waltzing Matilda" (karaoke style) and asked to give keywords that relate to at least five negative distressing experiences and an equal number of neutral experiences from the same period. The recording and the keywords will be used to derive the stimuli that are used in the functional MRI tasks (Pre-Post CBCTi). The screening visit is concluded with a demonstration on how to collect data at-home.

Both groups will be asked to perform a week of at-home assessment during 4 timepoints: T0 (baseline), T1 (2 months post-baseline), T2 (4 months post-baseline) and T3 (12 months post-baseline). During the week of at-home assessments, the participants complete questionnaires, keep a sleep diary, and wear an actigraphy-watch, and light and temperature sensor (across 7 days). They are also asked to complete at least four overnight polysomnographic recordings using an EEG headband. At Pre and Post-CBCTi only, they also complete a salivary melatonin collection protocol.

At Pre and Post-CBCTi (i.e., T0 and T1 for immediate group - T1 and T2 for delayed group) , participants are invited to Macquarie University/Woolcock Institute to undergo overnight sleep studies and neuroimaging sessions.

The CBCTi program will be given online via secure platforms and recruitment will primarily be through social media advertisements. The study will be coordinated from the Woolcock Institute of Medical Research, Sydney, Macquarie Park, New South Wales, 2109, Australia.

Inclusion Criteria:

• (A or B) and (C) A. Diagnosis of insomnia disorder (DSM-5-TR) B. Insomnia Severity Index (ISI) score ≥ 10 C. Generalized Anxiety Disorder (GAD-7) score ≥ 10
• All sexes and genders.
• Between 18 and 45 years of age.
• Able to provide informed consent.
• Proficient in English.

Exclusion Criteria:

x Sleep or circadian disorder other than insomnia (e.g., hypersomnolence, periodic limb movement disorder, advanced or delayed sleep phase disorder, moderate to severe sleep apnoea disorder based on previous sleep study with an apnea-hypopnea index ≥ 15 and/or finger-pulse oximetry oxygen desaturation index (ODI) ≥ 10).

• Current or history of neurological disorders (e.g., stroke, brain injury).
• Current or history of bipolar disorder, psychosis, or moderate to severe obsessive-compulsive disorder.
• Current uncontrolled mental health disorders requiring specialist care, other than major depression and anxiety disorders.
• Centrally active agents or presence of medical condition that may affect participation.
• Pregnancy or actively trying to conceive, or lactating.
• Shift work for at least 2 shifts per week in the past 3 months (i.e., work between 21:00 and 6:00).
• Travel across time zones over 3 hours difference in the previous 30 days (will require a 1-day adjustment period per hour of time zone travelled).
• Unwilling to know about potential incidental findings.
• No consent or adherence to instructions for any part of the study protocol.

All study team members have access to the dataset. Other Woolcock-affiliated staff may also request access to the non-identifiable dataset, which will be considered by the principal investigator and co-investigators. A copy of the non-identifiable dataset may be requested by academic collaborators not affiliated with the Woolcock through a data request form, which outlines the investigators, aims and hypotheses, data to be included, a statistical analysis plan, ethics approval, and security measures.

Researchers responsible for randomization and data-analysis will be blinded to the study arms.