The time of year can be a factor too. Lots of people have a degree of Seasonal Affective Disorder due to the short, gloomy days and the low angle of the sunlight in winter. And your meds should definitely be reviewed....I can't even imagine being on the same meds in the same dosages for that many years (but then, I've never been stable for more than a few months).

See your doctor ASAP. You deserve to feel better than this.