Learned about this condition in Psychology? Forgot the name?

Hey I'm taking Intro to Psych right now, and a couple weeks ago, my teacher briefly mentioned this mental condition where one is basically bipolar during the year... and the season is what affects it. For example, one person could be fine, dandy, happy in the summer and spring months but be depressed even to the point of suicidal in the winter... what is that called? Cause I think I may have a mild case of this. Thanks so much for your help.