I have known people who lied about their health if they wanted a day off work, or to get out of an invitation.
I have also known people who conveniently have a genuine miagrane or upset stomach when they don't want to do something or other, These people genuinely believe they are unlucky, even although to the rest of us it looks as if there is a phsyco-somatic aspect to these sudden attacks.
Some of course are suffering from whatever form of indisposition anxiety or nerves brings on.
I was brought up never to lie about my health, and belong to a generation that soldiered on through colds, sore throats etc and thereby probably infected others at work.
I was also brought up to believe that once you had accepted an invitation, you had to turn up at the event, however little you felt like it, and that invitations from casual acquaintances could be refused on the grounds that you had a prior engagement, but close friends or family was a different kettle of fish. You turned up, behaved yourself, and left when the first guests started making tracks if you were bored stiff.
Our children and grandchildren's generations tend to make no bones about making up some thin excuse if they just don't feel like going to a party, etc.