Sanjay Gupta thinks stroke or seizure is less likely (able to walk away), see about 5 min mark.
He said long list of possibilities but offered up like "parkinsonian and meds were wearing off". He had a good insight. He said his aides didn't seem surprised by it implying this may be happening more than just the past 2 episodes.
IMO time to give McConnell & Feinstein the gold watch retirement party.
https://www.youtube.com/watch?v=CN39Ukn3788