I feel in some cases that mood shifts can often affect financial spending because, when you are feeling down, you tend to look for things that will boost your mood, and in most cases, that tends to be buying something you have been wanting for a while or just buying something to cheer you up, without thinking about whether you can afford it or not.
I know I have done this in the past, felt down and have bought myself something without looking into whether it will affect my budget. I have learned over the years to hold back from that now and instead turn to something else, such as music, to help rather than spending money.