Yeah, pleasant it isn't. It's now 10 hours since I swabbed myself and I can still sort of feel it (though it's at the 'sort of feels like I want to sneeze' level and has been for a while). Not the mouth so much as the nostrils. And as a friend pointed out on FB, the self-testing instructions seem to suggest going a lot less far up the nose than the testing by actual medics does.