[Epona]

Think of it like this.
Celebrating midwinter (and in fact all seasons) is an ancient tradition going back to a time when there were no clocks or calendars. It was very important to societies reliant on their own agriculture to know when to start ploughing their plots of land and sowing their seeds. So they watched the phases of the moon and the stars, and length of sunlight during the day, and had festivals at certain times to mark the beginning of, in this instance, ploughing time. It served as a reminder to the whole community that they must soon start to plough their fields in order to have a crop next summer.
These events do not have to be imbued with mysticism. Of course the other purpose of a midwinter festival is to cheer everyone up at a time when life is hard, cold and wet, when there may be scarcity.
Of course to people with little knowledge of biology and cosmology, these events and the turning of the seasons did take on a mystical element, but it's not compulsory.
Celebrate it with this in mind, and enjoy yourself!