this happens to me, as well. it's not every day, and not with all toothpastes, but i definitely go through phases when it happens every time i brush- morning or evening. like the first writer, i've also been celibate for many years, and pregnancy isn't the cause.
None of the above suggestions would have any bearing on my situation, as it's not a reaction merely to the taste or to the size of the brush. it starts
For me it happens:
-every time i use children's bubblegum flavored toothpaste.
-other bubblegum flavored things do not cause it.
-other flavors of toothpaste DO cause it.
-more often with gel than with paste.
-begins the moment the toothpaste touches my tongue. begins with VERY heavy salivating, and a nausea. -rinsing my mouth doesn't stop it.
-breathing deeply while bent over helps, but doesn't stop it. (salivating the whole time)
-if i do begin to retch, it's a tossup as to whether or not it ends in vomiting.
-in bad cases, my gag reflex will keep up for half an hour. in mild ones, only a couple minutes.
-i've found that quickly gargling with listerine helps to short-circuit the process, if i catch it before the gagging.
the reaction happens whether or not i'm menstruating or at any particular point in cycle.
i'm not on other medications or physical/mental health issues.
I have never come across ANYthing other than toothpaste which trigger this reaction.