How scary! My grandfather was my hero. His mind was very much intact, but his body failed him from time to time.
I think you should follow up with your Gramp's regular physician. He or she should have any reports available from the ER. The Emergency Room is there to get people out of immediate danger.
Grandpa could have had low blood pressure, low sugar levels, low potassium levels. It's hard to say. They ruled out the two most serious things, heart attack and stroke. He wasn't in imminent danger and didn't require admission, thankfully.
Like I said, follow up with his regular doctor today. They should examine him to see if there are any changes in his BP, pulse, oxygen levels, etc. They can order more tests to find out what may have happened.
My grandmother lived to 94. She was tiny and often had episodes of being whoozy or short of breath. She had a home health nurse come once a week to take her vitals, give her a Vitamin B shot, and monitor.
As she got older, she became more anxious so they had her on a low dose of anxiety medication which also made her feel whoozy from time to time.
My point is, the regular physician can try to figure out what occurred and what caused it. The emergecy room isn't necessarily there to provide a diagnosis unless someone has a compound fracture, a heart attack, etc.
The regular physician can get the ER reports and go from there to try to obtain a diagnosis.
I know it's frustrating, but your grandfather's regular physician is the one who needs to either order more tests or translate the ER's findings and go from there.
I have worked at two hospitals. I've also been a patient myself.
The best thing to do is immediately follow up with the regular physician and go from there.
Very, very best wishes to you and your dear grandfather.