(I have not been diagnosed with Seasonal Affective Disorder but hopefully I could confirm this with my doctor during my next visit. More on this after my introduction on SAD immediately below this line).
Mostly, I consider myself “sad”. I am sad not for any other particular reason other than having depression most often than not so I could say such a feeling will always be part and parcel of my existence. However, this sadness can take on different forms; and yes, in diverse portions of a year, if I should say so. And since depression as an illness is commonly tagged as a persistence in low moods that could happen along the lines of prolonged periods, then depression may also be dependent on seasons and not merely through social triggers. Thus, the environment can play a very active role in the existence of particular emotional downturns.
Apart from depression we may be fairly acquainted with—including those exhibited in patients with bipolar disorder and others—there is one that is mainly dependent on the shifting of seasons, weather, and even miniscule ones such as transitions between temperatures. This may be loosely dubbed as Seasonal Affective Disorder, or S.A.D: commonly misunderstood but to those who suffer from it, an undeniable struggle that requires a lot of time and effort to curb or say, at the least, endure.
According to Mayo Clinic’s online article about SAD, it is “a type of depression that’s related to changes in seasons.” Also apparently, it occurs at the same time every year, for it seems to be dependent on certain cycles. For people with SAD, depression hovers over them just in time when the holidays begin to commence (about September to January, even) or during summer months, depending on how the body reacts to seasonal stimuli. As in the case of depressive episodes, they undergo the usual symptoms: the feelings of inadequacy, bouts of anxiety, gaining or losing weight, overeating or refraining from food, a lack of focus, occasional forgetfulness, exhaustion, irregular or prolonged sleep, and a host of many others characteristic of depression and anxiety. It is with this that those suffering from the infirmity tend to have difficulty dealing with the pressures of the holidays, sometimes (albeit reluctantly, perhaps) resolving to withdraw from their usual routines or even from people who matter to them the most.
As in the case of many other mental illnesses, SAD in a person can be addressed when diagnosed properly. There are many forms of therapy available, even those applicable to other forms of depression (like talk therapy/counseling), and light therapy—considerably unique but this is supposed to alleviate the malady by “resetting one’s biological clock.” This form of therapeutic measure requires a light box that simulates daylight or even bright lights in order to re-condition the person’s emotions vis-a-vis the season in question. Now, does it only happen during the latter parts of the year, when the cold winds blow and blustery days are at hand? Not at all, for it could happen even during spring and summer, where everyone is expected to be perky and all the more enthusiastic to savor the transcendental cool and then warmed-up breeze (especially when icy drafts have subsided). The summer/spring SAD could be an offshoot of circadian rhythms not having been quite adept yet with the transition between fall and winter to spring and summer, thus more complications such as losing enough sleep, anxiety, agitation, among others. Moreover, there are issues about melatonin and serotonin: the former, when diminished, increases the risk of convoluted sleep patterns; while the latter, an aggravation of the negative mood. Even so, emotions affected by the seasons can be terribly laborious to deal with that, on the part of those who experience it, a fervent desire that said seasons shift as quickly as possible, to leave no more room for agony.
By all means, information about SAD is everywhere and that we only have to turn on computers or smartphones in order to access such. The only big problem (as well as in a multitude of other mental illness-related symptoms) is self-diagnosis. It does not mean that if our own depressive traits may be somehow at par with an actual medical verdict concerning a particular mental illness, it may be deemed as so in ourselves. In the case of SAD, it does not follow that a depressive or anxiety-filled episode recurring during either cold or warm months can be primordial evidence for anyone to claim exhibiting the illness. There are blood tests to be administered if there be any chance it may be hypothyroidism instead of the disorder in question, or that there may be other symptoms that need to be paid attention to so as to rule out any possibility of a different medical interpretation. This would ring true in my situation as well: I begin to be jittery during the holidays, I dislike revelry and festive moods during certain special days (e.g. Christmas and New Year’s), and that I would feel relatively wearisome every November or December. So do I have SAD? I am not privy to that. My doctor knows best and all I have to do is confer with her, ask questions, and share my experiences in order to have that proper diagnosis.
 Mayo Clinic. “Seasonal Affective Disorder (SAD)”. https://www.mayoclinic.org/diseases-conditions/seasonal-affective-disorder/symptoms-causes/syc-20364651.
 WebMD. “Seasonal Affective Disorder (SAD)”. https://www.webmd.com/mental-health/tc/seasonal-affective-disorder-sad-topic-overview#2
(N.B.: Click on the above links for more information about SAD)