1. ‘Anxiety’ Online version Oxford Dictionary Accessed June 2018
2. Ainsworth MDS (1991) Attachments and other affectional bonds across the life cycle. In: Parkes CM, Stevenson-Hinde J, Marris P (eds) Attachment across the life cycle. Routledge, London, pp 33–51
3. American Psychiatric Association (2013) Diagnostic and statistical manual of mental disorders, 5th edn. American Psychiatric Association, Washington, DC
4. Aston-Jones G, Gonzalez M, Doran S (2007) Role of the locus coeruleus-norepinephrine system in arousal and circadian regulation of the sleep-wake cycle. In: Ordway GA, Schwartz MA, Frazer A (eds) Brain norepinephrine: neurobiology and therapeutics. Cambridge UP, New York
5. Bandura A (1977) Social learning theory. Prentice Hall, Englewood Cliffs