I have never heard of fit to sit but that is what I was made to do when I had Covid. At my A and E there are arms on either side of the chairs to stop anyone lying down (it might not be deliberate design I guess)
They apologised to me after 14 hours of sitting/vomiting/crying/fainting. And because it was Covid A and E there was no one even wandering about. Also no water ever these days.
Once upon a time in A and E you had a bed type thing to lie on. Those were the days.
A nice nurse took me to one and told me I could lie there then another nurse made me go back to the chairs :(