Unfortunately, the capitalization kind of gives away the fact that the word “SAD” in the title is an acronym. If it wasn’t an acronym, it would be really bad grammar.
Anyway, I’ve never heard of SAD. It stands for “seasonal affective disorder” and is a condition which allegedly affects one’s mood in the winter months. It is said that the condition makes some people more susceptible to depression and can also lower the effectiveness of their brain.
My dad actually used to know someone who claimed that he had SAD. A few times he brought a lamp in to his office for use in phototherapy which is supposed to help with SAD. My mom has heard that SAD was caused by a vitamin D deficiency, in which case the phototherapy would make sense. You could also just take a higher dose of vitamin D.
A couple of recent studies have actually shown that perhaps SAD doesn’t exist and that your brain might work faster in the winter months. I don’t know whether or not it exists, but before I heard of it I took vitamin D because it helps your immune system, which is important in the winter.