Poor guy! My gelding got overheated at a ride this weekend. We hosed him with cold water for 40 minutes until his temp came back down and fed him as much soaked beet pulp as we could stuff him with and he seems back to himself now. Hope it's just overheating for you too!
Sending good and healing vibes your way.... just remember to flush that catheter more often.... once it clogs it's a pain to get going again! That vet bill is not bad in my opinion.... not sure where you are but that's pretty good for my area.