I’ve seen three similar scenarios at two different churches. At the first, someone had a seizure (close to the front row) and collapsed. There was an audible thump and it was a small church, so no doubt about it, everyone knew. In this case, two men helped the person out of the church and someone called an ambulance. The priest continued on with Mass without batting an eyelash - well, at least as far as I could tell since it was a TLM and his back was to us. It actually went pretty much how I expected it to.
The second episode was at an NO. It was a very hot day and someone fainted. The priest asked for “Dr. Insert Name” to attend to the person and then continued with Mass after pausing for maybe ten seconds to say that and see that people actually were helping.
The third episode was at the same church but a different priest. The person fainted, the priest stepped into the sacristy and called an ambulance, some people helped the person out the door, and then Mass went on. I’d say the pause was about a minute and a half that time.
Now personally, I feel that the priest’s duty is to say Mass. There are plenty of people around to help out the ill person. In two of the three cases above, there was at least one doctor in the congregation (I think two in one case). Almost everybody these days carries cell phones, so I don’t think that the priest needed to be the one to call (although, admittedly, he seemed to act faster than anybody else).
And in case anybody is interested, all three episodes had happy endings.