I for one would not want to leave the zone. For me, LARP is about having fun, and if you’re no longer within your zone of happiness, then you’re no longer having fun. If you want people to leave saying ‘I enjoyed that game’, then you need to keep them within the limits of their tolerance for discomfort. Otherwise, their primary goal will be for the game to end rather than to ‘win’.
There is a difference between physical and psychological discomfort. The level of each you can cope with before becoming unhappy is a personal thing - for instance, I’d put up with cold weather (physical) or a rollercoaster (psychological), but I’d not want to go as far as (eg) army SAS training or rape scenes. Some people enjoy getting scared (else why would anyone watch horror films?) but I don’t think anyone enjoys getting into real fear.
When it comes down to it, in LARP, you can always call ‘Time out’ if you’re not happy with the psychological or physical aspects of where you are, and all other players and the GM should respect this. If you get some advance warning of what to expect. then you can generally ensure that you never reach this position.