Aren't people who suffer from so-called "seasonal affective disorders" faking?

Not, Nyet, Nine, No. SAD is now referred to as Depressive Disorder with Seasonal Pattern in DSM 5. It is a subtype of major depression. Symptoms are very real. I guess you have never experienced the symptoms or you would know that Depressive Disorder with Seasonal Pattern is very real.
SAD. Real disorder similar to depression associated with shorter days of winter.
SAD. Seasonal affective disorder (also called sad) is a type of depression that occurs at the same time every year. If you're like most people with seasonal affective disorder, your symptoms start in the fall and may continue into the winter months, sapping your energy and making you feel moody. Less often, seasonal affective disorder causes depression in the spring or early summer.