I had bipolar disorder several years ago and I cured it with light therapy and a high salt diet (isotonic). The light therapy has an obvious connection to the circadian clock – it lengthens daylight. But it took me a while to find how salt was connected. I discovered that in the evening my urine sodium level rose dramatically. This implies that my sodium blood level falls at this time, probably in preparation for sleep. When my sodium level goes below a certain level it causes a condition called hyponatremia which includes mental symptoms. The high salt diet prevents me from going below that critical level and the extra evening light therapy slows down the loss of sodium during the evening hours.