Is it NORMAL, to get choked unconscious in a class/in a tournament?
No, getting choked out “once every couple of months or so” is not and should not be normal. If true, then that school needs to correct how it’s “teaching” its students.
At any school where students are getting choked out regularly (as in more than once a year or every few years) in or after class, someone is doing something wrong (either the choker or the chokee). Getting choked unconscious for an extended (or really any) amount of time puts the person at risk of losing brain cells.
While their are instances of people getting choked unconscious… There is a great number of times that it is due to error/carelessness…
An example was another instance of a chokee doing something wrong (not tapping fast enough). A year or so later, the black belt Renzo Gracie instructor  at the CUBJJ school mentioned above was demonstrating a move before the entire class and the white belt he was going through the motions of applying the choke on did not realize the choke had started and went out briefly for ~3-5 seconds. The “clock” choke  was one of those super-fast blood chokes, and he went out before anyone in the class even knew, then someone gasped, the instructor stopped the choke, and he very quickly woke up.