Whenever I get gum surgery or implant surgery from my grad-student
dentist, I always end up choking towards the end of the session - an
hour and a half or so...

I always seem to get a lot of saliva and/or crap from the surgery
(blood, etc.?) in my throat and I find it difficult to swallow and end
up coughing/choking. I do my best to control it as he is suturing or
finishing up but it becomes very uncomfortable.

Should I demand to let him let me get up and rinse/spit, or what?

I have only had this problem with my implant and related surgeries by
this grad-student dentist and I don't know if it's because I've never
had such long sessions before, or if it's his or the assistant's
inexperience in getting me "suctioned" properly or ...?

Yesterday I had the gums cut open to reveal the 4 implants I had in
July (to prepare for crowns, finally!) and I was choking like crazy at
one point so he said, "Do you need to rinse?" and before I could say
yes, he said "We're almost done..."...

so I waited... another HALF HOUR of choking!

I hate to be a difficult patient so I just put up with it, but this
seems somewhat abusive and in retrospect I think I should have
demanded to get up and spit...

What is a patient to do?