I haven't had surgery since I was a kid but I still remember how disorientated I felt coming round from it. Anesthetic is obviously powerful stuff, and I've heard people say how they felt disturbed by the after effects.
So maybe it was like other bad drug experiences which have been a trigger for lots of people with DP, and like them you may have started self-checking and becoming hyper-aware of any sensation or perception that might be unusual or strange, so remaining in an anxious state long after the drug has worn off. Do you think that's a possibility? I also think it's more common than realized that people can find the whole experience of a medical procedure traumatic.