I think this need to be sorted. :/ if it is true as if you would put anything to sleep it would wake up at some point
I know the reason is gameplay-related, but one could explain this away by saying... Dinosaurs need a sedative of absurd strength to put them out quickly, and it's required to counteract that with another agent to wake them, else their heart will just outright stop after a certain period of time.
I've always been pretty good at spinning stuff. This is the explanation I'm going with.