Yes, this is a real holiday.
No, I had never heard of it before, either.
On this day, people are supposed to make sweet gestures towards one another, particularly the romantically inclined.
Obviously, it is not nearly as well known as Valentine's Day. It is only recognized in some states in the Midwest and a couple in the northeast. Some suggest that this is a made up holiday to boost sales of sweets for candy companies.
Perhaps, although since it is not so well known, perhaps we can stick with sweet gestures, without the commercialization. We sure could use more days like that, where we get away from taking so many things, and so many people, for granted.
So, Happy Sweetest Day!