Possibly a stroke or serious episode of hypoglycemia. Could be diabetic, on insulin or just have problems with low blood sugar events. Confusion, slurred speech can precede fainting in either scenario.
Could also include dehydration. and that could be the case for Hillary. Politicians often avoid water so as not to have to run to the bathroom. Women who have had children often have the problem of leakage. I know I have to be careful when I go out, but at least have the option of running to the bathroom without embarrassing myself in front of an audience.
Hubert Humphrey who ran against Nixon was known for making long speeches, and also died of bladder cancer. Don’t know if there was cause and effect, but it is something to think about. At any rate many people are chronically dehydrated which is especially harmful as you get older. It is easy to check. Your urine should be a very pale yellow like a manila file folder. Bright yellow or darker and you need to drink more water. Coffee does not count.
After a previous fainting episode Dayton complained of pain in his lower back. Note he took a large slug of water before going down. Wonder if it is something so simple as too many anticholergenics for something like IBS or Crohn's or even a vasovagal disorder. A hard swallow of water would be just the ideal trigger for the latter.