I would say more than unpleasant, more like vicious as well as judgemental regarding something you know nothing about.
Directly and publicly accusing someone of lying, based on incomplete knowledge of all the circumstances, and especially when it could be a disciplinary matter, would in itself be disciplinary where I work.
On the basis of one bitter person's account (the OP's), you would basically be acting in a way to get someone sacked because you THINK you know everything when you clearly don't. Read all the comments on here about sciatica from people who actually know about it, from a medical point of view not just the anecdotal "I had it once & was OK" or "it only took me 2 weeks to get better".
Consider the difference between a visit once to the shops, lasting maybe an hour, compared to working in an office or on a ward for 8 hours non stop. And bad pain is exhausting in itself, if someone managed an hour shopping in the kind of pain I've been in sometimes then they would most likely be wiped out for the next day or two.
But you go on making assumptions about whether someone is really fit to work or not, and accuse them publicly in the work place, and get your warm fuzzies about having shown how inconsiderate, tough & uncompromising you are and showing how you automatically assume the worst of everyone.