I would also like to note that I keep my chinchilla usually between 73F and 76F, and he will rarely see 80F. Although this is not best practice he has no problems and there is a calculated risk. I do notice that his behavior changes above 76 and his activity levels goes way down as it approaches 80F but if it does get there you are going to have to extra precautions because there is a risk of heat stress related death and it's really hard on them.
There is a tipping point and activity can easily push them over it and sometimes there is no return. If you think your chinchilla is having a seizure from heat stress first aid is to dip their lower half into room temperature water and then dry them off as best as possible while keeping their temperature as stable as possible. (Do not shock them with cold or it can kill them especially when their fur is wet) and call your vet to have them assess for organ damage.
When things get hot I recommend a target of 76F with 80F as a hard limit (unless you can go below that. In my room it's not always possible). Under cooler conditions try to keep the room around 73F.