Inclusion Criteria:  Hong Kong residents aged 18-59 years Cantonese language fluency A global Insomnia Severity Index (ISI) score of 10 or higher [A cutoff score of 10 was optimal (86.1% sensitivity and 87.7% specificity) for detecting insomnia cases (Morin, Belleville, Bélanger & Ivers, 2011)] A willingness to provide informed consent and comply with the trial protocol  Exclusion Criteria:  have major psychiatric, medical or neurocognitive disorders that make participation infeasible or interfere with the adherence to intervention previous suicide attempt, severe active suicidal ideation with a specific plan, severe self-harm, active substance abuse, or a history of psychosis. having cardiovascular diseases that affect the measure of heart rate variability having severe lung infections, central respiratory failure, electrolyte imbalance, fever and other diseases affecting the heart activity having with other organic diseases, previous history of arrhythmias (atrial fibrillation and frequent premature beats), hyperthyroidism, history of syncope and autonomic nervous system dysfunction have insomnia due to specific medical conditions, side effects of medication intake or other sleep disorders change in medication or its dosage 2 weeks before the baseline measurement