Kind of feeling depressed

And why is that? Seem like when you are tired, all attempts to try to stay positive tend to be halved, which kind of result in a downturn. Not sure if is the thought of long period of working ahead, or is the thought of walking down the path of time and realise that whatever you missed you will never have the chance to get back again. And even though it's almost the weekdays didn't manage to salvage much hope.