Maybe FakeBoobsRule can come reassure you if he sees this. I may tweak your title to pique his interest. This is quite literally the very medical alley he walks.

I suspect you're going to have conscious sedation, IV Valium or something like it. Tell your doctor what and how much you smoked. Be honest. He can crank back the benzodiazapine if he needs to and crank up the O2. And if he feels more comfortable doing so, he can reschedule you, which you want him to make a fully informed choice on, thus the advice about complete candor. I rather doubt that'll happen.

Tell me you've followed the non-per-os (nothing by mouth) instructions and haven't eaten a big meal or drunk a lot of after-midnight fluid, at least.