The more nefarious aspect is that people can think themselves sick; it's awful watching a group of mutually reinforcing hypochondriacs work themselves up from a

The more nefarious aspect is that people can think themselves sick; it's awful watching a group of mutually reinforcing hypochondriacs work themselves up from a minor sniffle or bit of dust in the eye to full incapacitation and dosing themselves with every over-the-counter snake oil imaginable.