there can be a host of reasons for people to get depressed, and what may depress someone may not do so for others, and vice versa. also, before i say anything else, i will just reiterate the fact that depression is a certified mental health concern that needs professional attention. some of the most common reasons for depression include heartbreak, death or departure of a loved one (could even be a pet), failure to get a job or loss of a job, financial stress, pregnancy and birth of a baby, health conditions. however, sometimes, there is no particular cause for depression. there have been many times when i have felt low and sad without really having a specific reason...
There are numerous reasons to be depressed. One can even get depressed on the reasons which generally are not considered to be depressed. Like, I am a woman who has ,touchwood, everything fine going on in her life, but I still get depressed and sometimes reasons are apparent and sometimes, I myself do not understand why I am depressed. So, reasons for depression are not stated. One can be depressed for any known or unknown reason.
it could be due to a lot of factors like events which caught you in surprise. or even unknown accumulated events which upsets you. do seek help if possible. talk to someone about it