Some just feel it as lack of energy and others again have more serious symptoms such as bigger appetite, felling sad, sleeping bad and so on.
I have been working with people with winter depressions through my education (social study) and through my work but I also know what winter depression feels like on a personal level because I too suffer from it almost every year.
Since I can't use any medication (they just don't sit well with me at all) I've been researching other means to ease the symptoms and found some VERY easy to follow and effective ways:-)
-After all it's all about getting those endorphines running through your body, right?!
ps. Sorry for not using the right turns for all the "happy hormones" I just don't know the names in english:-P
Stay safe and have a great winter!