Heat stroke/exhaustion/intolerance can provoke those symptoms. INgestion of something bad could too. Good thing you are Vetting. Did Vet ask for urine and poop samples? WE just had an "episode" too, which is now over, not resolved really, as we don't know for sure what caused it. ONe thing Vet told me to do was feed smaller meals, four instead of two, and if kibble then mix it with water to form a gruel to keep hydrated. My Holistic/Integrative Vet said NO meds to stop vomit or poop as both are the body's attempt to rid itself of something that should not be in it. Good luck at the Vet's today.
ETA: Does he have a temperature?