Notes

This book gives general information. It isn't medical advice, and it can't tell you whether any symptom of yours matters. If you're worried about a symptom, speak to a GP, a pharmacist or NHS 111. In an emergency call 999. The NHS services I describe are those for England as I found them in September 2026. Arrangements differ elsewhere in the UK and abroad, and they change.

I've kept sources out of the chapters where I could so they read easily. Here they are by chapter, with the limits I'm aware of. Unless I say otherwise, I read the published summary of each paper and not the full text. I checked each paper for a retraction or correction notice in September 2026. One has a published correction, which I mention below. Where a chapter isn't listed, it rests on my own reasoning. That includes chapters 1, 10 apart from one reference, 12, 13 and 19. The person in the examples is invented, along with the twitch, the forum post, the headache, the mole and the marks on the card. I've left the rare disease unnamed on purpose.

Before you start. The description of health anxiety and the advice on when to see a GP are from the NHS page "Health anxiety", last reviewed in November 2023. Advice on 999 and 111 is from the NHS pages "When to call 999" and "When to use NHS 111 online or call 111".

Chapter 1. What the NHS says about twitches is from its page "Twitching eyes and muscles". The list of features is mine.

Chapter 2. Starcevic and Berle, "Cyberchondria: towards a better understanding of excessive health-related Internet use", Expert Review of Neurotherapeutics 13, 2013, pages 205 to 213. Researchers call the habit cyberchondria, a word I've kept out of the chapters. Doherty-Torstrick, Walton and Fallon, "Cyberchondria: parsing health anxiety from online behavior", Psychosomatics 57, 2016, pages 390 to 400. The 731 participants were volunteers recalling how past searches had made them feel, so the study can't show that searching caused the feelings. The authors say their finding needs repeating in controlled experiments. The list of four needs is mine.

Chapter 3. Semigran, Linder, Gidengil and Mehrotra, "Evaluation of symptom checkers for self diagnosis and triage: audit study", BMJ 351, 2015, h3480. The study is ten years old and the tools will have changed. I haven't found a comparable test of open web searching. The account of what a doctor does is general knowledge.

Chapter 4. White and Horvitz, "Cyberchondria: studies of the escalation of medical concerns in Web search", ACM Transactions on Information Systems 27, 2009, article 23. That the authors worked at Microsoft is general knowledge and isn't in the summary I read. Search engines have changed a good deal since 2009, and some now put official health information first. Tversky and Kahneman, "Availability: a heuristic for judging frequency and probability", Cognitive Psychology 5, 1973, pages 207 to 232. My three suggestions about why searches lean towards serious conditions are reasoning and haven't been tested.

Chapter 5. Lucock, Morley, White and Peake, "Responses of consecutive patients to reassurance after gastroscopy", BMJ 315, 1997, pages 572 to 575. It was a small study with one consultant and sixty patients. Te Poel, Baumgartner, Hartmann and Tanis, "The curious case of cyberchondria: a longitudinal study on the reciprocal relationship between health anxiety and online health information seeking", Journal of Anxiety Disorders 43, 2016, pages 32 to 40. There were 5,322 respondents. The two-way relationship didn't appear in the subgroup whose health anxiety was already at a clinical level, though the authors think searching may still help to keep it going. The idea that reassurance brings short relief and strengthens the urge comes from the cognitive behavioural account of health anxiety associated with Paul Salkovskis and Hilary Warwick. I've described it in my own words from general knowledge and haven't read their 1986 paper.

Chapter 6. Fergus, "Cyberchondria and intolerance of uncertainty", Cyberpsychology, Behavior, and Social Networking 16, 2013, pages 735 to 739. My account of why the search stops at the frightening answer is an observation with no study behind it.

Chapter 7. Semigran and colleagues as above. Across the twenty-three checkers, appropriate advice was given in 80 per cent of emergency cases and in 33 per cent of cases where self-care would have been reasonable. That people search to talk themselves out of going is my observation.

Chapter 8. McAteer, Elliott and Hannaford, "Ascertaining the size of the symptom iceberg in a UK-wide community-based survey", British Journal of General Practice 61, 2011, pages e1 to e11. The survey went to 2,474 adults aged 18 to 60, and the mean was 3.66 symptoms in two weeks. The NHS statements are from its pages on health anxiety and on twitching. What I say about checking is reasoning, apart from the point about pulse, which follows from the NHS statement that anxiety can cause a racing heartbeat.

Chapter 9. Tubbs, Fernandez, Grandner, Perlis and Klerman, "The mind after midnight: nocturnal wakefulness, behavioral dysregulation, and psychopathology", Frontiers in Network Physiology 1, 2022, article 830338. It's a hypothesis paper. Palmer and colleagues, "Sleep loss and emotion: a systematic review and meta-analysis of over 50 years of experimental research", Psychological Bulletin 150, 2024, pages 440 to 463. The first two reasons in the chapter are mine.

Chapter 10. Semigran as above. I know of no good evidence yet on artificial intelligence chat assistants and health worry, and the chapter says so.

Chapter 11. The NHS list is from its health anxiety page. Lucock as above. "Safety netting" is a standard term in general practice, which I state from general knowledge.

Chapter 14. White and Horvitz as above. Everything else is my own reckoning.

Chapter 15. The one look is my arrangement of NHS advice and hasn't been tested. The wording about 999 and 111 is the NHS's. The instructions for a twitch are from the NHS page on twitching. That pharmacists can be consulted without an appointment is general knowledge.

Chapter 16. The diary, the gradual reduction, the two-column table, the headache example and the advice to distract yourself are from the self-help section of the NHS page on health anxiety. The twenty-minute delay, moving the phone, and the request to a partner are mine. They resemble what therapists recommend, and I haven't sourced them.

Chapter 17. Gollwitzer and Sheeran, "Implementation intentions and goal achievement: a meta-analysis of effects and processes", Advances in Experimental Social Psychology 38, 2006, pages 69 to 119. The rule and its parts haven't been tested together, and what I say to expect is my expectation and not a finding.

Chapter 18. Tyrer and colleagues, "Clinical and cost-effectiveness of cognitive behaviour therapy for health anxiety in medical patients: a multicentre randomised controlled trial", Lancet 383, 2014, pages 219 to 225. The journal published a correction to this paper in the same issue, and I haven't seen what it changed. The figures I give are from the summary, 13.9 per cent against 7.3 per cent reaching normal levels at one year. Newby and McElroy, "The impact of internet-delivered cognitive behavioural therapy for health anxiety on cyberchondria", Journal of Anxiety Disorders 69, 2020, article 102150. There were 41 people in each group, and the comparison group received information, monitoring and clinical support. Treatment options and self-referral are from the NHS health anxiety page. The advice for a child under five is from the NHS pages on 111. What I say about pregnancy and maternity units is general knowledge.

Chapter 19. What the NHS says about headaches is from its page "Headaches".