Glad Harvey is getting the meds he needs - I have alot of experience with this;
Yes, he needs the meds and I am glad your VET figured on getting the seizures under control.... too many seizures will lead to brain damage and possible stroke.
The cause may always be unknown. Someitmes they just never figure out what is going on. Keep a watch on his levels every month. You will learn how to manage the levels and get little to No seizure activity.
I run a Doggie Hotel and was a nurse for 17 years. I have a number of guest that need seizure meds or insulin injections. No biggie for me.
Seeing a grand mal seizure can be upsetting. As time goes by, you VET will have the levels regulated and you won't see too many seizures.
The Valium is by rectum? Correct...? This is placed into the rectal area only if the pet has grand mal ( very large seizure lasting over 60 seconds?)
Anyway, if you or anyone else has questions for me: Visit me and ask away... Best Wishes and Don't be afraid.