Regrettably I've been in an opposite situation. I often used to get genuinely unwell when having to visit the in-laws, if I was already not feeling too well the stress, the car journey, I've always had a tendency to car sickness, and not being able to sleep when I needed to sometimes used to send me over the edge into a fully blown migraine. Thankfully since I no longer have to do this I don't think I've had a migraine since. If I'd been able to have an early night and wake up refreshed I would probably have been ok or at least no migraine.
I've never had a non genuine sickie at work, in fact the last over 20 years of working because it was flexible and part time, I'd I wasn't well I'd just do what I needed to when I felt better
My old doc was a Highland Scots and he said that sometimes he would have a day off school to go fishing if he needed what we now call a mental health day. And actually I agree with him. Presenteeism is not good for the employer or the employee. If for whatever reason someone is stressed a day off could help reset things and get the work done when it's needed and the employee will feel better for it and be better able to do their job.
I think that going in when you're not really well enough is far too common and good for nobody
Maybe the King could say he can't get travel insurance, we all know what it's like with preexisting conditions and age, especially travelling to the US. If he became ill out there how much would that cost the British taxpayer?