To me, this just sounds likes a typical post-ictal state. My son's seizures will only last for a few minutes, but the post-ictal confusion can last for a half-hour or more. Don't feel so guilty! I would have done the same thing. You should believe the doctor, not the nurse who may not be familiar with your son's case.
My daughter is 2 1/2 years old and started having seizures at 9 months old. she has complex partial seizures and she will normally fall asleep for at least 2-3 hours after she has a seizure. We told her neurologist about this in the beginning and he said it was very normal for people to sleep for awhile after they have a seizure. He said that it gives time for the brain to recharge itself after a seizure. So, if she falls asleep afterwards....I will just let her sleep as long as she wants but I lay her down where I can keep an eye on her (usually on the coach in our living room). We have had to give her the diastat several times when her seizures were to close together without any recovery inbetween. Never because she fell asleep afterwards. I hope this helps!!!!!!!!
One thing I don't think people consider when someone has a seizure is the brain recovers one side at a time after seizures. Usually the side that controls hearing and seeing comes back first but the side that does the talking takes another 10 minutes. This used to be my biggest frustration because people would feel I just didn't want to talk but I would have given anything to communicate right away. A lot of times I just closed my eyes and fell asleep to eliminate the worst part as far as I'm concerned.
It can be difficult to tell when a seizure stops (of course it can also be quite easy too depending on the seizure and post-ictal presentation). Unfortunately unless your ER can quickly get an EEG going they're just going to be guessing too (hopefully they'll have educated guesses, but they're not usually seizure experts in the ER).
I would recommend videoing any strange seizures or post ictal periods so you can show your neurologist, they should be able to give the best advice.
If your son has more of these seizure types he'll hopefully develop a normal pattern that will help you recognize when his seizure has stopped. For example if after a partial seizure he always bounces back after 30 minutes then maybe 30 minutes is how long you wait before seeking additional help.
Over the years I've developed a pretty good (but not perfect) sixth sense for detecting when my daughter's seizures have stopped. I don't know that they'll help you much (my daughter's post-ictal isn't usually what you describe) but my "has my daughter's seizure ended" checklist is located here: