@Erased_CitizenIf they do decide to use a general anaesthetic then ask if you can talk to the anaesthetist - they are quite used to people with worries and should be able to put your mind - at least a little bit - at rest.
Blimey, the NHS is working fast today. Just sat down to lunch and my phone starts ringing. Can't answer but let it go to voicemail. It's the radiology department following up about the requested scan from the phone appointment earlier on.