It sounds to me as if there was a failure to communicate fully with you, so you didn't realise exactly what was going to happen and that, not surprisingly , caused you distress.
Here's a leaflet from Guys hospital (my father had open heart surgery here and they were, I have to say excellent)
From what you have said it seems to be a similar sequence of events to those you describe, have a look and see. A patient with this leaflet would know in advance what was to happen. They also include a statement about letting them know if you feel uncomfortable.
bottom of page 9
https://www.guysandstthomas.nhs.uk/...ar/having-a-permanent-pacemaker-implanted.pdf