It's possible he messed up the dosage. What he gave you wasn't good anymore. Or something else I'm not even thinking of.

The fact that he gave you something else that time, and that you've never had that experience again would make me believe he thought it was a fault in the product he initially gave you.

Ah thank you! That's super interesting. What an interesting job Anaesthetists have. I'm very greatful to mine, I always feel looked after when in his hands.