I brush my teeth in bed and swallow the toothpaste at the end. According to the chemical fact sheet swallowing my toothpaste is well within osha defined limits for sodium flouride, and people who live in places with naturally more fluoridated water than where I am are exposed for far more than I am. so I really don't think there is any health concern. I have been doing it for a decade now and I have no symptoms of over exposure. I find it greatly helps me fall asleep if I don't have to get out of bed to brush.
It skips a trip to the bathroom, no more "Oh, I forgot to brush teeth when already in bed". Weirdly enough I think it makes sense and is convenient but I personally won't do it because of the swallowing part.
For anyone curious, toothpaste has 1,000 to 1,500 ppm fluoride and tap water typically has ~1 ppm or less. Assuming OP swallowed a pea sized quantity of toothpaste (which is the reccommended amount for brushing) the amount of fluoride in that toothpaste would be about equivalent to drinking a cup of tap water.
There is about 0.15 to 0.2 grams of fluoride in a full tube of toothpaste. The LD50 in rats is about 60 mg/kg which is probably reasonably close to that of humans. i.e within an order of magnitude. Lets say the average person weighs 80 kg. That LD50 is about 4.8 grams for a single dose or about 20 to 30 full tubes of toothpaste. So while downing a full tube of toothpaste in one sitting will absolutely make you sick, it wont kill you. And thats hundreds of times the reccommended amount of toothpaste. That said I would not advise doing it for obvious reasons.