ANSWER

A volatile oil compound in chamomile is thought to be responsible for its mild sedative effects. Chamomile in the form of an aqueous extract has been frequently used as a mild sedative to calm nerves and help in stress-relieving .

Below are the related studies/articles:

Chamomile-A-herbal-medicine-of-the-past-with-bright-future

Chamomile-Matricaria-recutita-May-Have-Antidepressant-Activity-in-Anxious-Depressed-Humans-An-Exploratory-Study

Chamomile-Matricaria-recutita-Anthemis-nobilis

Herbal medicine for depression, anxiety and insomnia – A review of psychopharmacology and clinical evidence

Pharmacological-Properties-of-Matricaria-recutita-A-Review

Substance-related-Anxiety-Disorder-and-how-Amino-Acids-and-Herbs-may-be-utilized-in-treatment