However, the nose also contains erectile tissue, and this may also become engorged during arousal, triggering the need to sneeze.

There is a condition known as honeymoon rhinitis, in which men and women experience nasal stuffiness during sex.

honeymoon rhinitis. Try to remember that condition

I never have any warning. It can be so embarrassing.

ever hear of people who cry- for some unemotional chemical reason- after sex?

This article sounds like it is describing a form of synesthesia, at least it seems so to me.